Light-emitting element, light-emitting device, electronic device, and lighting device

ABSTRACT

A light-emitting element having a long lifetime is provided. A light-emitting element exhibiting high emission efficiency in a high luminance region is provided. A light-emitting element includes a light-emitting layer between a pair of electrodes. The light-emitting layer contains a first organic compound, a second organic compound, and a phosphorescent compound. The first organic compound is represented by a general formula (G0). The molecular weight of the first organic compound is greater than or equal to 500 and less than or equal to 2000. The second organic compound is a compound having an electron-transport property. In the general formula (G0), Ar 1  and Ar 2  each independently represent a fluorenyl group, a spirofluorenyl group, or a biphenyl group, and Ar 3  represents a substituent including a carbazole skeleton.

This application is a continuation of U.S. application Ser. No.15/999,406, filed Aug. 20, 2018, now pending, which is a continuation ofU.S. application Ser. No. 15/228,557, filed Aug. 4, 2016, now U.S. Pat.No. 10,069,076, which is a continuation of U.S. application Ser. No.13/957,082, filed Aug. 1, 2013, now U.S. Pat. No. 9,412,962, whichclaims the benefit of foreign priority applications filed in Japan asSerial No. 2013-045127 on Mar. 7, 2013, and Serial No. 2012-172944 onAug. 3, 2012, all of which are incorporated by reference.

TECHNICAL FIELD

The present invention relates to a light-emitting element utilizingelectroluminescence (EL) (also referred to as an EL element), alight-emitting device, an electronic device, and a lighting device.

BACKGROUND ART

In recent years, research and development have been extensivelyconducted on EL elements. In a basic structure of EL elements, a layercontaining a light-emitting substance is provided between a pair ofelectrodes. By applying voltage to this element, light emission from thelight-emitting substance can be obtained.

Since such an EL element is of self-light-emitting type, it isconsidered that the EL element has advantages over a liquid crystaldisplay in that visibility of pixels is high, backlight is not required,and so on and is therefore suitable as flat panel display elements. Inaddition, it is also a great advantage that the EL element can bemanufactured as a thin and lightweight element. Furthermore, very highspeed response is also one of the features of such an element.

Since EL elements can be formed in the form of a film, they make itpossible to provide planar light emission. Therefore, large-areaelements can be easily formed. This feature is difficult to obtain withpoint light sources typified by incandescent lamps and LEDs or linearlight sources typified by fluorescent lamps. Thus, EL elements also havegreat potential as planar light sources which can be applied to lightingdevices and the like.

EL elements can be broadly classified according to whether thelight-emitting substance is an organic compound or an inorganiccompound. In the case of an organic EL element in which a layercontaining an organic compound as the light-emitting substance isprovided between a pair of electrodes, application of a voltage to thelight-emitting element causes injection of electrons from the cathodeand holes from the anode into the layer containing the organic compound,and thus a current flows. The injected electrons and holes then lead theorganic compound to its excited state, whereby light emission isobtained from the excited organic compound.

The excited state of an organic compound can be a singlet excited stateand a triplet excited state, and light emission from the singlet excitedstate (S*) is referred to as fluorescence, and light emission from thetriplet excited state (T*) is referred to as phosphorescence.

In improving element characteristics of such a light-emitting element,there are a lot of problems which depend on a substance, and in order tosolve the problems, improvement of an element structure, development ofa substance, and the like have been carried out. For example, PatentDocument 1 discloses an organic light-emitting element including a mixedlayer containing an organic low molecular hole-transport substance, anorganic low molecular electron-transport substance, and a phosphorescentdopant.

REFERENCE

[Patent Document 1] Japanese Translation of PCT InternationalApplication No. 2004-515895

DISCLOSURE OF INVENTION

The development of organic EL elements leaves room for improvement interms of emission efficiency, reliability, cost, and the like.

For practical use of displays or lights with organic EL elements,organic EL elements are required to have longer lifetimes and exhibithigher emission efficiency in a high luminance region, for example.

Thus, an object of one embodiment of the present invention is to providea light-emitting element having a long lifetime. Another object of oneembodiment of the present invention is to provide a light-emittingelement exhibiting high emission efficiency in a high luminance region.

Another object of one embodiment of the present invention is to providea light-emitting device, an electronic device, and a lighting deviceeach having high reliability by using the above light-emitting element.

A light-emitting element in one embodiment of the present inventionincludes a light-emitting layer between a pair of electrodes, and thelight-emitting layer contains a first organic compound, a second organiccompound, and a phosphorescent compound. The first organic compound is atertiary amine and has a structure in which two substituents including afluorene skeleton, a spirofluorene skeleton, or a biphenylene skeletonand one substituent including a carbazole skeleton are each bonded to anitrogen atom directly. The molecular weight of the first organiccompound is greater than or equal to 500 and less than or equal to 2000.The second organic compound is a compound having an electron-transportproperty. With the light-emitting layer having such a structure, thelight-emitting element can have a long lifetime. In addition, thelight-emitting element can exhibit high emission efficiency in a highluminance region.

Specifically, one embodiment of the present invention is alight-emitting element including a light-emitting layer between a pairof electrodes. The light-emitting layer contains a first organiccompound, a second organic compound, and a phosphorescent compound. Thefirst organic compound is represented by a general formula (G0). Themolecular weight of the first organic compound is greater than or equalto 500 and less than or equal to 2000. The second organic compound is acompound having an electron-transport property.

In the general formula (G0), Ar¹ and Ar² each independently represent asubstituted or unsubstituted fluorenyl group, a substituted orunsubstituted spirofluorenyl group, or a substituted or unsubstitutedbiphenyl group, and Ar³ represents a substituent including a carbazoleskeleton.

Another embodiment of the present invention is a light-emitting elementincluding a light-emitting layer between a pair of electrodes. Thelight-emitting layer contains a first organic compound, a second organiccompound, and a phosphorescent compound. The first organic compound isrepresented by a general formula (G1). The molecular weight of the firstorganic compound is greater than or equal to 500 and less than or equalto 2000. The second organic compound is a compound having anelectron-transport property.

In the general formula (G1), Ar¹ and Ar² each independently represent asubstituted or unsubstituted fluorenyl group, a substituted orunsubstituted spirofluorenyl group, or a substituted or unsubstitutedbiphenyl group; α represents a substituted or unsubstituted phenylenegroup or a substituted or unsubstituted biphenyldiyl group; n represents0 or 1; and A represents a substituted or unsubstituted 3-carbazolylgroup.

Another embodiment of the present invention is a light-emitting elementincluding a light-emitting layer between a pair of electrodes. Thelight-emitting layer contains a first organic compound, a second organiccompound, and a phosphorescent compound. The first organic compound isrepresented by a general formula (G2). The molecular weight of the firstorganic compound is greater than or equal to 500 and less than or equalto 2000. The second organic compound is a compound having anelectron-transport property.

In the general formula (G2), Ar¹ and Ar² each independently represent asubstituted or unsubstituted fluorenyl group, a substituted orunsubstituted spirofluorenyl group, or a substituted or unsubstitutedbiphenyl group; R¹ to R⁴ and R¹¹ to R¹⁷ each independently representhydrogen, an alkyl group having 1 to 10 carbon atoms, an unsubstitutedphenyl group or a phenyl group having as a substituent at least onealkyl group having 1 to 10 carbon atoms, or an unsubstituted biphenylgroup or a biphenyl group having as a substituent at least one alkylgroup having 1 to 10 carbon atoms; Ar⁴ represents an alkyl group having1 to 10 carbon atoms, an unsubstituted phenyl group or a phenyl grouphaving as a substituent at least one alkyl group having 1 to 10 carbonatoms, an unsubstituted biphenyl group or a biphenyl group having as asubstituent at least one alkyl group having 1 to 10 carbon atoms, or anunsubstituted terphenyl group or a terphenyl group having as asubstituent at least one alkyl group having 1 to 10 carbon atoms.

Another embodiment of the present invention is a light-emitting elementincluding a light-emitting layer between a pair of electrodes. Thelight-emitting layer contains a first organic compound, a second organiccompound, and a phosphorescent compound. The first organic compound isrepresented by a general formula (G3). The molecular weight of the firstorganic compound is greater than or equal to 500 and less than or equalto 2000. The second organic compound is a compound having anelectron-transport property.

In the general formula (G3), Ar¹ and Ar² each independently represent asubstituted or unsubstituted fluorenyl group, a substituted orunsubstituted spirofluorenyl group, or a substituted or unsubstitutedbiphenyl group; R¹ to R⁴, R¹¹ to R¹⁷, and R²¹ to R²⁵ each independentlyrepresent hydrogen, an alkyl group having 1 to 10 carbon atoms, anunsubstituted phenyl group or a phenyl group having as a substituent atleast one alkyl group having 1 to 10 carbon atoms, or an unsubstitutedbiphenyl group or a biphenyl group having as a substituent at least onealkyl group having 1 to 10 carbon atoms.

In the above embodiments of the present invention, it is preferable thatAr¹ and Ar² in each of the general formulae (G0) to (G3) eachindependently represent a substituted or unsubstituted 2-fluorenylgroup, a substituted or unsubstituted spiro-9,9′-bifluoren-2-yl group,or a biphenyl-4-yl group.

In the above embodiment of the present invention, it is preferable thata hole-transport layer be provided in contact with the light-emittinglayer, the hole-transport layer contain a third organic compound, thethird organic compound be represented by the general formula (G0), andthe molecular weight of the third organic compound be greater than orequal to 500 and less than or equal to 2000.

In the general formula (G0), Ar¹ and Ar² each independently represent asubstituted or unsubstituted fluorenyl group, a substituted orunsubstituted spirofluorenyl group, or a substituted or unsubstitutedbiphenyl group, and Ar³ represents a substituent including a carbazoleskeleton.

In the above embodiment of the present invention, it is preferable thata hole-transport layer be provided in contact with the light-emittinglayer, the hole-transport layer contain a third organic compound, thethird organic compound be represented by the general formula (G1), andthe molecular weight of the third organic compound be greater than orequal to 500 and less than or equal to 2000.

In the general formula (G1), Ar¹ and Ar² each independently represent asubstituted or unsubstituted fluorenyl group, a substituted orunsubstituted spirofluorenyl group, or a substituted or unsubstitutedbiphenyl group; a represents a substituted or unsubstituted phenylenegroup or a substituted or unsubstituted biphenyldiyl group; n represents0 or 1; and A represents a substituted or unsubstituted 3-carbazolylgroup.

In the above embodiment of the present invention, it is preferable thata hole-transport layer be provided in contact with the light-emittinglayer, the hole-transport layer contain a third organic compound, thethird organic compound be represented by the general formula (G2), andthe molecular weight of the third organic compound be greater than orequal to 500 and less than or equal to 2000.

In the general formula (G2), Ar¹ and Ar² each independently represent asubstituted or unsubstituted fluorenyl group, a substituted orunsubstituted spirofluorenyl group, or a substituted or unsubstitutedbiphenyl group; R¹ to R⁴ and R¹¹ to R¹⁷ each independently representhydrogen, an alkyl group having 1 to 10 carbon atoms, an unsubstitutedphenyl group or a phenyl group having as a substituent at least onealkyl group having 1 to 10 carbon atoms, or an unsubstituted biphenylgroup or a biphenyl group having as a substituent at least one alkylgroup having 1 to 10 carbon atoms; Ar⁴ represents an alkyl group having1 to 10 carbon atoms, an unsubstituted phenyl group or a phenyl grouphaving as a substituent at least one alkyl group having 1 to 10 carbonatoms, an unsubstituted biphenyl group or a biphenyl group having as asubstituent at least one alkyl group having 1 to 10 carbon atoms, or anunsubstituted terphenyl group or a terphenyl group having as asubstituent at least one alkyl group having 1 to 10 carbon atoms.

In the above embodiment of the present invention, it is preferable thata hole-transport layer be provided in contact with the light-emittinglayer, the hole-transport layer contain a third organic compound, thethird organic compound be represented by the general formula (G3), andthe molecular weight of the third organic compound be greater than orequal to 500 and less than or equal to 2000.

In the general formula (G3), Ar¹ and Ar² each independently represent asubstituted or unsubstituted fluorenyl group, a substituted orunsubstituted spirofluorenyl group, or a substituted or unsubstitutedbiphenyl group; R¹ to R⁴, R¹¹ to R¹⁷, and R²¹ to R²⁵ each independentlyrepresent hydrogen, an alkyl group having 1 to 10 carbon atoms, anunsubstituted phenyl group or a phenyl group having as a substituent atleast one alkyl group having 1 to 10 carbon atoms, or an unsubstitutedbiphenyl group or a biphenyl group having as a substituent at least onealkyl group having 1 to 10 carbon atoms.

In the above embodiments of the present invention, it is preferable thatthe third organic compound be identical to the first organic compound.

In the above embodiments of the present invention, it is preferable thata combination of the first organic compound and the second organiccompound form an exciplex.

In the above embodiments of the present invention, it is preferable thatthe compound having the electron-transport property be a π-electrondeficient heteroaromatic compound. Examples of the π-electron deficientheteroaromatic compound include compounds including a quinoxalineskeleton, a dibenzoquinoxaline skeleton, a quinoline skeleton, apyrimidine skeleton, a pyrazine skeleton, a pyridine skeleton, a diazoleskeleton, or a triazole skeleton.

Another embodiment of the present invention is a light-emitting deviceincluding the above-described light-emitting element in a light-emittingportion. Another embodiment of the present invention is an electronicdevice including the light-emitting device in a display portion. Anotherembodiment of the present invention is a lighting device including thelight-emitting device in a light-emitting portion.

Since the light-emitting element in one embodiment of the presentinvention has a long lifetime, a light-emitting device having highreliability can be obtained. Similarly, an electronic device and alighting device having high reliability can be obtained by employing oneembodiment of the present invention.

In addition, since the light-emitting element in one embodiment of thepresent invention exhibits high emission efficiency in a high luminanceregion, a light-emitting device with high emission efficiency can beobtained. Similarly, an electronic device and a lighting device withhigh emission efficiency can be obtained by employing one embodiment ofthe present invention.

Note that the light-emitting device in this specification includes, inits category, an image display device with a light-emitting element. Inaddition, the light-emitting device includes all the following modules:a module in which a connector, such as an anisotropic conductive film ora tape carrier package (TCP), is attached to a light-emitting device; amodule in which a printed wiring board is provided at the end of a TCP;and a module in which an integrated circuit (IC) is directly mounted ona light-emitting device by a chip-on-glass (COG) method. Furthermore,light-emitting devices that are used in lighting equipment and the likeshall also be included.

One embodiment of the present invention can provide a light-emittingelement having a long lifetime. By using the light-emitting element, alight-emitting device, an electronic device, and a lighting device eachhaving high reliability can be provided. One embodiment of the presentinvention can also provide a light-emitting element exhibiting highemission efficiency in a high luminance region. By using thelight-emitting element, a light-emitting device, an electronic device,and a lighting device each with high emission efficiency can beprovided.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A to 1F each illustrate an example of a light-emitting element inone embodiment of the present invention.

FIG. 2A illustrates an example of a light-emitting element in oneembodiment of the present invention, and FIGS. 2B and 2C illustrate aconcept of an exciplex in one embodiment of the present invention.

FIGS. 3A and 3B illustrate an example of a light-emitting device in oneembodiment of the present invention.

FIGS. 4A and 4B illustrate an example of a light-emitting device in oneembodiment of the present invention.

FIGS. 5A to 5E each illustrate an example of an electronic device.

FIGS. 6A and 6B illustrate examples of lighting devices.

FIG. 7 illustrates a light-emitting element in examples.

FIG. 8 shows luminance-current efficiency characteristics oflight-emitting elements in Example 1.

FIG. 9 shows voltage-luminance characteristics of the light-emittingelements in Example 1.

FIG. 10 shows luminance-external quantum efficiency characteristics ofthe light-emitting elements in Example 1.

FIGS. 11A and 11B show results of reliability tests of thelight-emitting elements in Example 1.

FIG. 12 shows luminance-current efficiency characteristics oflight-emitting elements in Example 2.

FIG. 13 shows voltage-luminance characteristics of the light-emittingelements in Example 2.

FIG. 14 shows luminance-power efficiency characteristics of thelight-emitting elements in Example 2.

FIG. 15 shows luminance-external quantum efficiency characteristics ofthe light-emitting elements in Example 2.

FIG. 16 shows results of reliability tests of the light-emittingelements in Example 2.

FIG. 17 shows luminance-current efficiency characteristics oflight-emitting elements in Example 3.

FIG. 18 shows voltage-luminance characteristics of the light-emittingelements in Example 3.

FIG. 19 shows luminance-power efficiency characteristics of thelight-emitting elements in Example 3.

FIG. 20 shows luminance-external quantum efficiency characteristics ofthe light-emitting elements in Example 3.

FIGS. 21A and 21B show ¹H NMR charts ofN-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine(abbreviation: PCBBiF).

FIGS. 22A and 22B show an absorption spectrum and an emission spectrumof PCBBiF in a toluene solution of PCBBiF.

FIGS. 23A and 23B show an absorption spectrum and an emission spectrumof a thin film of PCBBiF.

FIGS. 24A and 24B show ¹H NMR charts ofN-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9′-spirobi[9H-fluoren]-2-amine(abbreviation: PCBBiSF).

FIGS. 25A and 25B show an absorption spectrum and an emission spectrumof PCBBiSF in a toluene solution of PCBBiSF.

FIGS. 26A and 26B show an absorption spectrum and an emission spectrumof a thin film of PCBBiSF.

FIG. 27 shows voltage-current characteristics of light-emitting elementsin Example 4.

FIG. 28 shows luminance-external quantum efficiency characteristics ofthe light-emitting elements in Example 4.

FIG. 29 shows emission spectra of the light-emitting elements in Example4.

FIG. 30 shows results of reliability tests of the light-emittingelements in Example 4.

FIG. 31 shows luminance-current efficiency characteristics oflight-emitting elements in Example 5.

FIG. 32 shows voltage-luminance characteristics of the light-emittingelements in Example 5.

FIG. 33 shows luminance-external quantum efficiency characteristics ofthe light-emitting elements in Example 5.

FIG. 34 shows results of reliability tests of the light-emittingelements in Example 5.

FIG. 35 shows luminance-current efficiency characteristics oflight-emitting elements in Example 6.

FIG. 36 shows voltage-luminance characteristics of the light-emittingelements in Example 6.

FIG. 37 shows luminance-external quantum efficiency characteristics ofthe light-emitting elements in Example 6.

FIG. 38 shows results of reliability tests of the light-emittingelements in Example 6.

FIG. 39 shows luminance-current efficiency characteristics of alight-emitting element in Example 7.

FIG. 40 shows voltage-luminance characteristics of the light-emittingelement in Example 7.

FIG. 41 shows luminance-external quantum efficiency characteristics ofthe light-emitting element in Example 7.

FIG. 42 shows results of a reliability test of the light-emittingelement in Example 7.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments will be described in detail with reference to the drawings.Note that the present invention is not limited to the followingdescription, and it will be easily understood by those skilled in theart that various changes and modifications can be made without departingfrom the spirit and scope of the present invention. Therefore, thepresent invention should not be construed as being limited to thedescription in the following embodiments. Note that in the structures ofthe invention described below, the same portions or portions havingsimilar functions are denoted by the same reference numerals indifferent drawings, and description of such portions is not repeated.

Embodiment 1

In this embodiment, light-emitting elements in one embodiment of thepresent invention will be described with reference to FIGS. 1A to 1F.

Light-emitting elements given in this embodiment as examples eachinclude a pair of electrodes and a layer containing a light-emittingorganic compound (EL layer) between the pair of electrodes.

A light-emitting element illustrated in FIG. 1A includes an EL layer 203between a first electrode 201 and a second electrode 205. In thisembodiment, the first electrode 201 serves as an anode, and the secondelectrode 205 serves as a cathode.

When a voltage higher than the threshold voltage of the light-emittingelement is applied between the first electrode 201 and the secondelectrode 205, holes are injected to the EL layer 203 from the firstelectrode 201 side and electrons are injected to the EL layer 203 fromthe second electrode 205 side. The injected electrons and holes arerecombined in the EL layer 203 and a light-emitting substance containedin the EL layer 203 emits light.

The EL layer 203 includes at least a light-emitting layer 303. In thelight-emitting element in this embodiment, the light-emitting layer 303contains a first organic compound, a second organic compound, and aphosphorescent compound.

In this embodiment, the phosphorescent compound is used as thelight-emitting substance that is a guest material. One of the first andsecond organic compounds, the content of which is higher than that ofthe other in the light-emitting layer, is called a host material wherethe guest material is dispersed.

In the light-emitting layer of the light-emitting element in thisembodiment, the content of the host material is higher than that of theguest material. When the guest material is dispersed in the hostmaterial, the crystallization of the light-emitting layer can besuppressed. Further, it is possible to suppress concentration quenchingdue to high concentration of the guest material, and thus thelight-emitting element can have higher emission efficiency.

The first organic compound is a tertiary amine and has a structure inwhich two substituents including a fluorene skeleton, a spirofluoreneskeleton, or a biphenylene skeleton and one substituent including acarbazole skeleton are each bonded to a nitrogen atom directly. Themolecular weight of the first organic compound is greater than or equalto 500 and less than or equal to 2000. The second organic compound is acompound having an electron-transport property.

In the tertiary amine, a biphenyl group, a fluorenyl group, or aspirofluorenyl group is introduced as the substituent directly bonded tothe nitrogen atom, instead of a phenyl group or an alkylphenyl grouphaving a simple structure. Therefore, the tertiary amine is chemicallystable, which enables a stable light-emitting element having a longlifetime to be easily obtained with high reproducibility. The tertiaryamine also includes a carbazole skeleton and therefore has high thermalstability and improves reliability. The tertiary amine further includesa fluorenylamine skeleton, a spirofluorenylamine skeleton, or abiphenylamine skeleton, and therefore has a high hole-transport propertyand a high electron-blocking property. In addition, the tertiary aminehas high triplet excitation energy compared with an amine including anaphthalene skeleton or the like, and therefore has an excellentexciton-blocking property. Accordingly, leakage of electrons ordiffusion of excitons can be prevented even in a high luminance region,and thus the light-emitting element can exhibit high emissionefficiency.

Materials which can be used as the first organic compound, the secondorganic compound, and the phosphorescent compound contained in thelight-emitting layer 303 will be described in detail below.

<First Organic Compound>

The first organic compound is represented by the general formula (G0),and the molecular weight of the first organic compound is greater thanor equal to 500 and less than or equal to 2000.

In the general formula (G0), Ar¹ and Ar² each independently represent asubstituted or unsubstituted fluorenyl group, a substituted orunsubstituted spirofluorenyl group, or a substituted or unsubstitutedbiphenyl group, and Ar³ represents a substituent including a carbazoleskeleton.

In the case where the fluorenyl group, the spirofluorenyl group, or thebiphenyl group has a substituent in the general formula (G0), examplesof the substituent include an alkyl group having 1 to 10 carbon atoms,an unsubstituted phenyl group or a phenyl group having as a substituentat least one alkyl group having 1 to 10 carbon atoms, an unsubstitutedbiphenyl group or a biphenyl group having as a substituent at least onealkyl group having 1 to 10 carbon atoms, and an unsubstituted terphenylgroup or a terphenyl group having as a substituent at least one alkylgroup having 1 to 10 carbon atoms. The compound represented by thegeneral formula (G0) and having any of these substituents is less likelyto have low hole-transport, electron-blocking, and exciton-blockingproperties than (or can have hole-transport, electron-blocking, andexciton-blocking properties as high as) a compound not having thesubstituent.

Examples of Ar³ include a substituted or unsubstituted(9H-carbazol-9-yl)phenyl group, a substituted or unsubstituted(9H-carbazol-9-yl)biphenyl group, a substituted or unsubstituted(9H-carbazol-9-yl)terphenyl group, a substituted or unsubstituted(9-aryl-9H-carbazol-3-yl)phenyl group, a substituted or unsubstituted(9-aryl-9H-carbazol-3-yl)biphenyl group, a substituted or unsubstituted(9-aryl-9H-carbazol-3-yl)terphenyl group, a substituted or unsubstituted9-aryl-9H-carbazol-3-yl group, and the like. Specific examples of arylgroups include an unsubstituted phenyl group or a phenyl group having asa substituent at least one alkyl group having 1 to 10 carbon atoms, anunsubstituted biphenyl group or a biphenyl group having as a substituentat least one alkyl group having 1 to 10 carbon atoms, an unsubstitutedterphenyl group or a terphenyl group having as a substituent at leastone alkyl group having 1 to 10 carbon atoms, and the like. Note that inthe case where Ar³ has a substituent, examples of the substituentinclude an alkyl group having 1 to 10 carbon atoms, an unsubstitutedphenyl group or a phenyl group having as a substituent at least onealkyl group having 1 to 10 carbon atoms, an unsubstituted biphenyl groupor a biphenyl group having as a substituent at least one alkyl grouphaving 1 to 10 carbon atoms, an unsubstituted terphenyl group or aterphenyl group having as a substituent at least one alkyl group having1 to 10 carbon atoms, and the like. Each of these substituents cansuppress the impairment of the high hole-transport, electron-blocking,and exciton-blocking properties of the compound represented by thegeneral formula (G0).

It is preferable that the first organic compound contained in thelight-emitting layer 303 be represented by the following general formula(G1).

In the general formula (G1), Ar¹ and Ar² each independently represent asubstituted or unsubstituted fluorenyl group, a substituted orunsubstituted spirofluorenyl group, or a substituted or unsubstitutedbiphenyl group; a represents a substituted or unsubstituted phenylenegroup or a substituted or unsubstituted biphenyldiyl group; n represents0 or 1; and A represents a substituted or unsubstituted 3-carbazolylgroup.

Examples of specific structures of a in the general formula (G1) areshown by structural formulae (1-1) to (1-9).

It is further preferable that the first organic compound contained inthe light-emitting layer 303 be represented by the following generalformula (G2).

In the general formula (G2), Ar¹ and Ar² each independently represent asubstituted or unsubstituted fluorenyl group, a substituted orunsubstituted spirofluorenyl group, or a substituted or unsubstitutedbiphenyl group; R¹ to R⁴ and R¹¹ to R¹⁷ each independently representhydrogen, an alkyl group having 1 to 10 carbon atoms, an unsubstitutedphenyl group or a phenyl group having as a substituent at least onealkyl group having 1 to 10 carbon atoms, or an unsubstituted biphenylgroup or a biphenyl group having as a substituent at least one alkylgroup having 1 to 10 carbon atoms; Ar⁴ represents an alkyl group having1 to 10 carbon atoms, an unsubstituted phenyl group or a phenyl grouphaving as a substituent at least one alkyl group having 1 to 10 carbonatoms, an unsubstituted biphenyl group or a biphenyl group having as asubstituent at least one alkyl group having 1 to 10 carbon atoms, or anunsubstituted terphenyl group or a terphenyl group having as asubstituent at least one alkyl group having 1 to 10 carbon atoms.

It is particularly preferable that the first organic compound containedin the light-emitting layer 303 be represented by the following generalformula (G3).

In the general formula (G3), Ar¹ and Ar² each independently represent asubstituted or unsubstituted fluorenyl group, a substituted orunsubstituted spirofluorenyl group, or a substituted or unsubstitutedbiphenyl group; R¹ to R⁴, R¹¹ to R¹⁷, and R²¹ to R²⁵ each independentlyrepresent hydrogen, an alkyl group having 1 to 10 carbon atoms, anunsubstituted phenyl group or a phenyl group having as a substituent atleast one alkyl group having 1 to 10 carbon atoms, or an unsubstitutedbiphenyl group or a biphenyl group having as a substituent at least onealkyl group having 1 to 10 carbon atoms.

It is preferable that Ar¹ and Ar² each independently represent asubstituted or unsubstituted 2-fluorenyl group, a substituted orunsubstituted spiro-9,9′-bifluoren-2-yl group, or a biphenyl-4-yl group.A tertiary amine including any of these skeletons is preferable becauseof its high hole-transport and electron-blocking properties, and itsexcellent exciton-blocking property due to its triplet excitation energyhigher than that of an amine including a naphthalene skeleton or thelike. Among biphenyl groups, fluorenyl groups, and spirofluorenylgroups, the ones with these sites of substitution are preferable becausethey are easy to synthesize and are inexpensiveness.

Examples of specific structures of R¹ to R⁴, R¹¹ to R¹⁷, and R²¹ to R²⁵in the general formulae (G2) and (G3) are shown by structural formulae(2-1) to (2-17). In the case where the fluorenyl group, thespirofluorenyl group, or the biphenyl group has a substituent in each ofthe above general formulae, examples of the substituent include an alkylgroup having 1 to 10 carbon atoms, an unsubstituted phenyl group or aphenyl group having as a substituent at least one alkyl group having 1to 10 carbon atoms, and an unsubstituted biphenyl group or a biphenylgroup having as a substituent at least one alkyl group having 1 to 10carbon atoms. As examples of specific structures of these, thesubstituents represented by the structural formulae (2-2) to (2-17) canbe given. Examples of specific structures of Ar⁴ in the general formula(G2) include substituents represented by the structural formulae (2-2)to (2-17).

Specific examples of the organic compound represented by the generalformulae (G0) include organic compounds represented by structuralformulae (101) to (142). Note that the present invention is not limitedto these examples.

<Second Organic Compound>

The second organic compound is a compound having an electron-transportproperty. As the compound having the electron-transport property, aπ-electron deficient heteroaromatic compound such as anitrogen-containing heteroaromatic compound, a metal complex having aquinoline skeleton or a benzoquinoline skeleton, a metal complex havingan oxazole-based or thiazole-based ligand, or the like can be used.

Specific examples include the following: metal complexes such asbis(10-hydroxybenzo[h]quinolinato)berylium(II) (abbreviation: BeBq₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III)(abbreviation: BAlq), bis(8-quinolinolato)zinc(II) (abbreviation: Znq),bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: Zn(BOX)₂), andbis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: Zn(BTZ)₂);heterocyclic compounds having a polyazole skeleton, such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ),1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation:CO11), 2,2′,2″-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole)(abbreviation: TPBI), and2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole(abbreviation: mDBTBIm-II); heterocyclic compounds having a quinoxalineskeleton or a dibenzoquinoxaline skeleton, such as2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-II), 7-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 7mDBTPDBq-II),6-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:6mDBTPDBq-II),2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II), and2-[3′-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mCzBPDBq); heterocyclic compounds having a diazineskeleton (a pyrimidine skeleton or a pyrazine skeleton), such as4,6-bis[3-(phenanthren-9-yl)phenyl]pyrimidine (abbreviation:4,6mPnP2Pm), 4,6-bis[3-(9H-carbazol-9-yl)phenyl]pyrimidine(abbreviation: 4,6mCzP2Pm), and4,6-bis[3-(4-dibenzothienyl)phenyl]pyrimidine (abbreviation:4,6mDBTP2Pm-II); heterocyclic compounds having a pyridine skeleton, suchas 3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (abbreviation: 35DCzPPy),1,3,5-tri[3-(3-pyridyl)phenyl]benzene (abbreviation: TmPyPB), and3,3′,5,5′-tetra[(m-pyridyl)-phen-3-yl]biphenyl (abbreviation: BP4mPy).Among the above materials, heterocyclic compounds having a quinoxalineskeleton or a dibenzoquinoxaline skeleton, heterocyclic compounds havinga diazine skeleton, and heterocyclic compounds having a pyridineskeleton are preferable because of their high reliability.

<Phosphorescent Compound>

Examples of phosphorescent compounds which can be used for thelight-emitting layer 303 are given here. Examples of phosphorescentcompounds having an emission peak at 440 nm to 520 nm include thefollowing: organometallic iridium complexes having a 4H-triazoleskeleton, such astris{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-yl-κN²]phenyl-κC}iridium(III)(abbreviation: [Ir(mpptz-dmp)₃]),tris(5-methyl-3,4-diphenyl-4H-1,2,4-triazolato)iridium(III)(abbreviation: [Ir(Mptz)₃], andtris[4-(3-biphenyl)-5-isopropyl-3-phenyl-4H-1,2,4-triazolato]iridium(III)(abbreviation: [Ir(iPrptz-3b)₃]); organometallic iridium complexeshaving a 1H-triazole skeleton, such astris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazolato]iridium(III)(abbreviation: [Ir(Mptz1-mp)₃]) andtris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazolato)iridium(III)(abbreviation: [Ir(Prptzl-Me)₃]); organometallic iridium complexeshaving an imidazole skeleton, such asfac-tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazole]iridium(III)(abbreviation: [Ir(iPrpmi)₃]) andtris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridinato]iridium(III)(abbreviation: [Ir(dmpimpt-Me)₃]); and organometallic iridium complexesin which a phenylpyridine derivative having an electron-withdrawinggroup is a ligand, such asbis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)tetrakis(1-pyrazolyl)borate (abbreviation: FIr6),bis[2-(4′,6′-difluorophenyl)pyridinato-N,C²′]iridium(III) picolinate(abbreviation: FIrpic),bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N,C^(2′)}iridium(III)picolinate (abbreviation: [Ir(CF₃ppy)₂(pic)]), andbis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)acetylacetonate (abbreviation: FIr(acac)). Among the above materials,the organometallic iridium complexes having a 4H-triazole skeleton areparticularly preferable because of their high reliability and highemission efficiency.

Examples of phosphorescent compounds having an emission peak at 520 nmto 600 nm include the following: organometallic iridium complexes havinga pyrimidine skeleton, such astris(4-methyl-6-phenylpyrimidinato)iridium(III) (abbreviation:[Ir(mppm)₃]), tris(4-t-butyl-6-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(tBuppm)₃]),(acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(mppm)₂(acac)]),(acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(tBuppm)₂(acac)]),(acetylacetonato)bis[4-(2-norbornyl)-6-phenylpyrimidinato]iridium(III)(endo- and exo-mixture) (abbreviation: [Ir(nbppm)₂(acac)]),(acetylacetonato)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidinato]iridium(III)(abbreviation: [Ir(mpmppm)₂(acac)]), and(acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III)(abbreviation: [Ir(dppm)₂(acac)]); organometallic iridium complexeshaving a pyrazine skeleton, such as(acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)(abbreviation: [Ir(mppr-Me)₂(acac)]) and(acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III)(abbreviation: [Ir(mppr-iPr)₂(acac)]); organometallic iridium complexeshaving a pyridine skeleton, such astris(2-phenylpyridinato-N,C^(2′))iridium(III) (abbreviation:[Ir(ppy)₃]), bis(2-phenylpyridinato-N,C²′)iridium(III) acetylacetonate(abbreviation: [Ir(ppy)₂(acac)]), bis(benzo[h]quinolinato)iridium(III)acetylacetonate (abbreviation: [Ir(bzq)₂(acac)]),tris(benzo[h]quinolinato)iridium(III) (abbreviation: [Ir(bzq)₃]),tris(2-phenylquinolinato-N,C²′)iridium(III) (abbreviation: [Ir(pq)₃]),and bis(2-phenylquinolinato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: [Ir(pq)₂(acac)]); and rare earth metal complexes such astris(acetylacetonato)(monophenanthroline)terbium(III) (abbreviation:[Tb(acac)₃(Phen)]). Among the above materials, the organometalliciridium complexes having a pyrimidine skeleton are particularlypreferable because of their distinctively high reliability and emissionefficiency.

Examples of phosphorescent compounds having an emission peak at 600 nmto 700 nm include the following: organometallic iridium complexes havinga pyrimidine skeleton, such asbis[4,6-bis(3-methylphenyl)pyrimidinato](diisobutyrylmethano)iridium(III)(abbreviation: [Ir(5mdppm)₂(dibm)]),bis[4,6-bis(3-methylphenyl)pyrimidinato](dipivaloylmethanato)iridium(III)(abbreviation: [Ir(5mdppm)₂(dpm)]), andbis[4,6-di(naphthalen-1-yl)pyrimidinato](dipivaloylmethanato)iridium(III)(abbreviation: [Ir(dlnpm)₂(dpm)]); organometallic iridium complexeshaving a pyrazine skeleton, such as(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: [Ir(tppr)₂(acac)]),bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III)(abbreviation: [Ir(tppr)₂(dpm)]), and(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: [Ir(Fdpq)₂(acac)]); organometallic iridium complexeshaving a pyridine skeleton, such astris(1-phenylisoquinolinato-N,C²′)iridium(III) (abbreviation:[Ir(piq)₃]) and bis(1-phenylisoquinolinato-N,C^(2′))iridium(III)acetylacetonate (abbreviation: [Ir(piq)₂(acac)]); platinum complexessuch as 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II)(abbreviation: PtOEP); and rare earth metal complexes such astris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III)(abbreviation: [Eu(DBM)₃(Phen)]) andtris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III)(abbreviation: [Eu(TTA)₃(Phen)]). Among the above materials, theorganometallic iridium complexes having a pyrimidine skeleton areparticularly preferable because of their distinctively high reliabilityand emission efficiency. Further, the organometallic iridium complexeshaving a pyrazine skeleton can provide red light emission with favorablechromaticity.

With the use of the above-described light-emitting layer containing thefirst organic compound, the second organic compound, and thephosphorescent compound, a light-emitting element having a long lifetimecan be manufactured. In addition, with the use of the light-emittinglayer, a light-emitting element exhibiting high emission efficiency in ahigh luminance region can be manufactured.

Further, by providing a plurality of light-emitting layers and makingemission colors of the light-emitting layers different, light emissionof a desired color can be obtained from the light-emitting element as awhole. For example, the emission colors of first and secondlight-emitting layers are complementary in a light-emitting elementhaving the two light-emitting layers, so that the light-emitting elementcan be made to emit white light as a whole. Note that the term“complementary” means color relationship in which an achromatic color isobtained when colors are mixed. That is, emission of white light can beobtained by mixture of light emitted from substances whose emissioncolors are complementary colors. Further, the same applies to alight-emitting element having three or more light-emitting layers. Notethat in a light-emitting element including a plurality of light-emittinglayers in one embodiment of the present invention, at least one of thelight-emitting layers has the above-described composition (containingthe first organic compound, the second organic compound, and thephosphorescent compound), and all the light-emitting layers may have theabove composition.

In addition to the light-emitting layer, the EL layer 203 may furtherinclude one or more layers containing any of a substance with a highhole-injection property, a substance with a high hole-transportproperty, a hole-blocking material, a substance with a highelectron-transport property, a substance with a high electron-injectionproperty, a substance with a bipolar property (a substance with highelectron- and hole-transport properties), and the like. A known materialcan be used for the EL layer 203. Either a low molecular compound or ahigh molecular compound can be used, and an inorganic compound may alsobe used.

A light-emitting element illustrated in FIG. 1B includes the EL layer203 between the first electrode 201 and the second electrode 205, and inthe EL layer 203, a hole-injection layer 301, a hole-transport layer302, a light-emitting layer 303, an electron-transport layer 304, and anelectron-injection layer 305 are stacked in this order from the firstelectrode 201 side.

A light-emitting element illustrated in FIG. 1C includes the EL layer203 between the first electrode 201 and the second electrode 205, andfurther includes an intermediate layer 207 between the EL layer 203 andthe second electrode 205.

A specific example of a structure of the intermediate layer 207 isillustrated in FIG. 1D. The intermediate layer 207 includes at least acharge-generation region 308. In addition to the charge-generationregion 308, the intermediate layer 207 may further include anelectron-relay layer 307 and an electron-injection buffer layer 306. InFIG. 1D, the light-emitting element includes the EL layer 203 over thefirst electrode 201, the intermediate layer 207 over the EL layer 203,and the second electrode 205 over the intermediate layer 207. Inaddition, as the intermediate layer 207 in FIG. 1D, theelectron-injection buffer layer 306, the electron-relay layer 307, andthe charge-generation region 308 are provided in this order from the ELlayer 203 side.

When a voltage higher than the threshold voltage of the light-emittingelement is applied between the first electrode 201 and the secondelectrode 205, holes and electrons are generated in thecharge-generation region 308, and the holes move into the secondelectrode 205 and the electrons move into the electron-relay layer 307.The electron-relay layer 307 has a high electron-transport property andimmediately transfers the electrons generated in the charge-generationregion 308 to the electron-injection buffer layer 306. Theelectron-injection buffer layer 306 lowers a barrier to electroninjection into the EL layer 203 and improves the efficiency of electroninjection into the EL layer 203. In this manner, electrons generated inthe charge-generation region 308 are injected into the LUMO (lowestunoccupied molecular orbital) level of the EL layer 203 through theelectron-relay layer 307 and the electron-injection buffer layer 306.

In addition, the electron-relay layer 307 can prevent reaction at theinterface between a substance contained in the charge-generation region308 and a substance contained in the electron-injection buffer layer306. Thus, it is possible to prevent interaction such as impairing thefunctions of the charge-generation region 308 and the electron-injectionbuffer layer 306.

As illustrated in light-emitting elements in FIGS. 1E and 1F, aplurality of EL layers may be stacked between the first electrode 201and the second electrode 205. In this case, the intermediate layer 207is preferably provided between the stacked EL layers. For example, thelight-emitting element illustrated in FIG. 1E includes the intermediatelayer 207 between a first EL layer 203 a and a second EL layer 203 b.The light-emitting element illustrated in FIG. 1F includes n EL layers(n is a natural number of 2 or more) and the intermediate layers 207, anintermediate layer 207 being between an m-th EL layer 203(m) and an(m+1)-th EL layer 203(m+1). Note that in a light-emitting element of oneembodiment of the present invention which includes a plurality of ELlayers, the above-described composition (containing the first organiccompound, the second organic compound, and the phosphorescent compound)is applied to at least one of the EL layers and may be applied to allthe EL layers.

The behaviors of electrons and holes in the intermediate layer 207provided between the EL layer 203(m) and the EL layer 203(m+1) will bedescribed. When a voltage higher than the threshold voltage of thelight-emitting element is applied between the first electrode 201 andthe second electrode 205, holes and electrons are generated in theintermediate layer 207, and the holes move into the EL layer 203(m+1)provided on the second electrode 205 side and the electrons move intothe EL layer 203(m) provided on the first electrode 201 side. The holesinjected into the EL layer 203(m+1) are recombined with electronsinjected from the second electrode 205 side, so that a light-emittingsubstance contained in the EL layer 203(m+1) emits light. Further, theelectrons injected into the EL layer 203(m) are recombined with holesinjected from the first electrode 201 side, so that a light-emittingsubstance contained in the EL layer 203(m) emits light. Thus, the holesand electrons generated in the intermediate layer 207 cause lightemission in different EL layers.

Note that the EL layers can be provided in contact with each other whenthese EL layers allow the same structure as the intermediate layer to beformed therebetween. For example, when the charge-generation region isformed over one surface of an EL layer, another EL layer can be providedin contact with the surface.

Further, by making emission colors of the EL layers different, lightemission of a desired color can be obtained from the light-emittingelement as a whole. For example, the emission colors of first and secondEL layers are complementary in a light-emitting element having the twoEL layers, so that the light-emitting element can be made to emit whitelight as a whole. The same applies to a light-emitting element havingthree or more EL layers.

FIGS. 1B to 1E can be used in an appropriate combination. For example,the intermediate layer 207 can be provided between the second electrode205 and the EL layer 203(n) in FIG. 1F.

Examples of materials which can be used for each layer will be givenbelow. Note that each layer is not limited to a single layer, and may bea stack of two or more layers.

<Anode>

The electrode serving as the anode (the first electrode 201 in thisembodiment) can be formed using one or more kinds of conductive metalsand alloys, conductive compounds, and the like. In particular, it ispreferable to use a material with a high work function (4.0 eV or more).Examples include indium tin oxide (ITO), indium tin oxide containingsilicon or silicon oxide, indium zinc oxide, indium oxide containingtungsten oxide and zinc oxide, graphene, gold, platinum, nickel,tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, and anitride of a metal material (e.g., titanium nitride).

When the anode is in contact with the charge-generation region, any of avariety of conductive materials can be used regardless of their workfunctions; for example, aluminum, silver, an alloy containing aluminum,or the like can be used.

<Cathode>

The electrode serving as the cathode (the second electrode 205 in thisembodiment) can be formed using one or more kinds of conductive metalsand alloys, conductive compounds, and the like. In particular, it ispreferable to use a material with a low work function (3.8 eV or less).Examples include aluminum, silver, an element belonging to Group 1 or 2of the periodic table (e.g., an alkali metal such as lithium or cesium,an alkaline earth metal such as calcium or strontium, or magnesium), analloy containing any of these elements (e.g., Mg—Ag or Al—Li), a rareearth metal such as europium or ytterbium, and an alloy containing anyof these rare earth metals.

Note that in the case where the cathode is in contact with thecharge-generation region, any of a variety of conductive materials canbe used regardless of its work function. For example, ITO, silicon, orindium tin oxide containing silicon oxide can be used.

The light-emitting element may have a structure in which one of theanode and the cathode is formed using a conductive film that transmitsvisible light and the other is formed using a conductive film thatreflects visible light, or a structure in which both the anode and thecathode are formed using conductive films that transmit visible light.

The conductive film that transmits visible light can be formed using,for example, indium oxide, ITO, indium zinc oxide, zinc oxide, or zincoxide to which gallium is added. Alternatively, a film of a metalmaterial such as gold, platinum, nickel, tungsten, chromium, molybdenum,iron, cobalt, copper, palladium, or titanium, or a nitride of any ofthese metal materials (e.g., titanium nitride) can be formed thin so asto have a light-transmitting property. Further alternatively, grapheneor the like may be used.

The conductive film that reflects visible light can be formed using, forexample, a metal material such as aluminum, gold, platinum, silver,nickel, tungsten, chromium, molybdenum, iron, cobalt, copper, orpalladium; an aluminum-containing alloy (aluminum alloy) such as analloy of aluminum and titanium, an alloy of aluminum and nickel, or analloy of aluminum and neodymium; or a silver-containing alloy such as analloy of silver and copper. An alloy of silver and copper is preferablebecause of its high heat resistance. Further, lanthanum, neodymium, orgermanium may be added to the metal material or the alloy.

The electrodes may be formed separately by a vacuum evaporation methodor a sputtering method. Alternatively, when a silver paste or the likeis used, a coating method or an inkjet method may be used.

<Hole-Injection Layer 301>

The hole-injection layer 301 contains a substance having a highhole-injection property.

Examples of the substance having a high hole-injection property includemetal oxides such as molybdenum oxide, titanium oxide, vanadium oxide,rhenium oxide, ruthenium oxide, chromium oxide, zirconium oxide, hafniumoxide, tantalum oxide, silver oxide, tungsten oxide, and manganeseoxide.

A phthalocyanine-based compound such as phthalocyanine (abbreviation:H₂Pc) or copper(II) phthalocyanine (abbreviation: CuPc) can also beused.

Further alternatively, it is possible to use an aromatic amine compoundwhich is a low molecular organic compound, such as4,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA),4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB),4,4′-bis(N-{4-[N′-(3-methylphenyl)-N′-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD),1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B),3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2), or3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1).

Further alternatively, it is possible to use a high molecular compoundsuch as poly(N-vinylcarbazole) (abbreviation: PVK),poly(4-vinyltriphenylamine) (abbreviation: PVTPA),poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](abbreviation: PTPDMA), orpoly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviation:Poly-TPD), or a high molecular compound to which acid is added, such aspoly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS)or polyaniline/poly(styrenesulfonic acid) (PAni/PSS).

The hole-injection layer 301 may serve as the charge-generation region.When the hole-injection layer 301 in contact with the anode serves asthe charge-generation region, any of a variety of conductive materialscan be used for the anode regardless of their work functions. Materialscontained in the charge-generation region will be described later.

<Hole-Transport Layer 302>

The hole-transport layer 302 contains a substance having a highhole-transport property. The substance having the high hole-transportproperty is a substance having a property of transporting more holesthan electrons, and is especially preferably a substance having a holemobility of 10⁻⁶ cm²/Vs or more.

For the hole-transport layer 302, any of the organic compoundsrepresented by the above general formulae (G0) to (G3) can be used. Whenany of the organic compounds represented by the above general formulae(G0) to (G3) is used for both the hole-transport layer 302 and thelight-emitting layer 303, it is possible to lower a hole-injectionbarrier and thus possible to not only increase emission efficiency butalso decrease a drive voltage. In other words, such a structure makes itpossible not only to maintain high emission efficiency in a highluminance region as described above but also to keep a drive voltagelow. As a result, a light-emitting element with little decrease in powerefficiency due to voltage loss even at high luminance, that is, alight-emitting element with high power efficiency (low powerconsumption) can be obtained. It is particularly preferable that thehole-transport layer 302 and the light-emitting layer 303 contain thesame organic compound in terms of the hole-injection barrier.

Other examples of the substance having a high hole-transport propertyare aromatic amine compounds such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB orα-NPB),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD), 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: BPAFLP),4,4′-bis[N-(9,9-dimethylfluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: DFLDPBi), and4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB).

Alternatively, it is possible to use a carbazole derivative such as4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP),9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation: CzPA),or 9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: PCzPA).

Further alternatively, it is possible to use an aromatic hydrocarboncompound such as 2-tert-butyl-9,10-di(2-naphthyl)anthracene(abbreviation: t-BuDNA), 9,10-di(2-naphthyl)anthracene (abbreviation:DNA), or 9,10-diphenylanthracene (abbreviation: DPAnth).

A high molecular compound such as PVK, PVTPA, PTPDMA, or Poly-TPD canalso be used.

<Electron-Transport Layer 304>

The electron-transport layer 304 contains a substance having a highelectron-transport property.

The substance having a high electron-transport property is an organiccompound having a property of transporting more electrons than holes,and is especially preferably a substance having an electron mobility of10⁻⁶ cm²/Vs or more.

For the electron-transport layer 304, the second organic compound (thecompound having the electron-transport property) contained in thelight-emitting layer 303 can be used.

A metal complex such as tris(8-quinolinolato)aluminum(III)(abbreviation: Alq) or tris(4-methyl-8-quinolinolato)aluminum(III)(abbreviation: Almq₃) can be used for the electron-transport layer 304.

Further, a heteroaromatic compound such as bathophenanthroline(abbreviation: BPhen), bathocuproine (abbreviation: BCP),3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: p-EtTAZ), or 4,4′-bis(5-methylbenzoxazol-2-yl)stilbene(abbreviation: BzOs) can be used.

Further, a high molecular compound such as poly(2,5-pyridinediyl)(abbreviation: PPy),poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)](abbreviation: PF-Py), orpoly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2′-bipyridine-6,6′-diyl)](abbreviation: PF-BPy) can be used.

<Electron-Injection Layer 305>

The electron-injection layer 305 contains a substance having a highelectron-injection property.

Examples of the substance having a high electron-injection propertyinclude an alkali metal, an alkaline earth metal, a rare earth metal,and a compound thereof (e.g., an oxide thereof, a carbonate thereof, anda halide thereof), such as lithium, cesium, calcium, lithium oxide,lithium carbonate, cesium carbonate, lithium fluoride, cesium fluoride,calcium fluoride, and erbium fluoride.

The electron-injection layer 305 may contain the above-describedsubstance having the high electron-transport property and a donorsubstance. For example, the electron-injection layer 305 may be formedusing an Alq layer containing magnesium (Mg). When the substance havinga high electron-transport property and the donor substance arecontained, the mass ratio of the donor substance to the substance havingthe high electron-transport property is preferably from 0.001:1 to0.1:1.

Examples of the donor substance include an alkali metal, an alkalineearth metal, a rare earth metal, and a compound thereof (e.g., an oxidethereof), such as lithium, cesium, magnesium, calcium, erbium,ytterbium, lithium oxide, calcium oxide, barium oxide, and magnesiumoxide; a Lewis base; and an organic compound such as tetrathiafulvalene(abbreviation: TTF), tetrathianaphthacene (abbreviation: TTN),nickelocene, or decamethylnickelocene.

<Charge-Generation Region>

The charge-generation region included in the hole-injection layer andthe charge-generation region 308 each contain a substance having a highhole-transport property and an acceptor substance (electron acceptor).The acceptor substance is preferably added so that the mass ratio of theacceptor substance to the substance having the high hole-transportproperty is from 0.1:1 to 4.0:1.

The charge-generation region is not limited to a structure in which asubstance having a high hole-transport property and an acceptorsubstance are contained in the same film, and may have a structure inwhich a layer containing a substance having a high hole-transportproperty and a layer containing an acceptor substance are stacked. Notethat in the case of a stacked-layer structure in which thecharge-generation region is provided on the cathode side, the layercontaining the substance having the high hole-transport property is incontact with the cathode, and in the case of a stacked-layer structurein which the charge-generation region is provided on the anode side, thelayer containing the acceptor substance is in contact with the anode.

The substance having the high hole-transport property is an organiccompound having a property of transporting more holes than electrons,and is especially preferably an organic compound having a hole mobilityof 10⁻⁶ cm²/Vs or more.

Specifically, it is possible to use the compound represented by theabove general formula (G0) or any of the substances having the highhole-transport property given as examples of substances that can be usedfor the hole-transport layer 302, e.g., aromatic amine compounds such asNPB and BPAFLP, carbazole derivatives such as CBP, CzPA, and PCzPA,aromatic hydrocarbon compounds such as t-BuDNA, DNA, and DPAnth, andhigh molecular compounds such as PVK and PVTPA.

Examples of the acceptor substance include halogen compounds such as7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ) and chloranil, cyano compounds such aspirazino[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile (abbreviation:PPDN) anddipyrazino[2,3-f:2′,3′-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile(abbreviation: HAT-CN), transition metal oxides, and oxides of metalsbelonging to Groups 4 to 8 of the periodic table. Specifically, vanadiumoxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide,tungsten oxide, manganese oxide, and rhenium oxide are preferablebecause of their high electron-accepting property. In particular,molybdenum oxide is preferable because of its stability in theatmosphere, low hygroscopic property, and ease of handling.

<Electron-Injection Buffer Layer 306>

The electron-injection buffer layer 306 contains a substance having ahigh electron-injection property. The electron-injection buffer layer306 facilitates electron injection from the charge-generation region 308into the EL layer 203. As the substance having the highelectron-injection property, any of the above-described materials can beused. Alternatively, the electron-injection buffer layer 306 may containany of the above-described substances having the high electron-transportproperty and donor substances.

<Electron-Relay Layer 307>

The electron-relay layer 307 immediately accepts electrons drawn out bythe acceptor substance in the charge-generation region 308.

The electron-relay layer 307 contains a substance having a highelectron-transport property. As the substance having the highelectron-transport property, a phthalocyanine-based material or a metalcomplex having a metal-oxygen bond and an aromatic ligand is preferablyused.

As the phthalocyanine-based material, specifically, it is possible touse CuPc, a phthalocyanine tin(II) complex (SnPc), a phthalocyanine zinccomplex (ZnPc), cobalt(II) phthalocyanine, β-form (CoPc), phthalocyanineiron (FePc), or vanadyl 2,9,16,23-tetraphenoxy-29H,31H-phthalocyanine(PhO-VOPc).

As the metal complex having a metal-oxygen bond and an aromatic ligand,a metal complex having a metal-oxygen double bond is preferably used. Ametal-oxygen double bond has an acceptor property; thus, electrons canbe transferred (donated and accepted) more easily.

As the metal complex having a metal-oxygen bond and an aromatic ligand,a phthalocyanine-based material is also preferably used. In particular,vanadyl phthalocyanine (VOPc), a phthalocyanine tin(IV) oxide complex(SnOPc), or a phthalocyanine titanium oxide complex (TiOPc) ispreferable because a metal-oxygen double bond is more likely to act onanother molecule in terms of a molecular structure and an acceptorproperty is high.

As the phthalocyanine-based material, a phthalocyanine-based materialhaving a phenoxy group is preferably used. Specifically, aphthalocyanine derivative having a phenoxy group, such as PhO-VOPc, ispreferably used. The phthalocyanine derivative having a phenoxy group issoluble in a solvent; thus, the phthalocyanine derivative has anadvantage of being easily handled during formation of a light-emittingelement and an advantage of facilitating maintenance of an apparatusused for film formation.

Examples of other substances having the high electron-transport propertyinclude perylene derivatives such as 3,4,9,10-perylenetetracarboxylicdianhydride (abbreviation: PTCDA), 3,4,9,10-perylenetetracarboxylicbisbenzimidazole (abbreviation: PTCBI),N,N′-dioctyl-3,4,9,10-perylenetetracarboxylic diimide (abbreviation:PTCDI-C8H), N,N′-dihexyl-3,4,9,10-perylenetetracarboxylic diimide(abbreviation: Hex PTC), and the like. Alternatively, it is possible touse a nitrogen-containing condensed aromatic compound such aspirazino[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile (abbreviation:PPDN), 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene(abbreviation: HAT(CN)₆), 2,3-diphenylpyrido[2,3-b]pyrazine(abbreviation: 2PYPR), or 2,3-bis(4-fluorophenyl)pyrido[2,3-b]pyrazine(abbreviation: F2PYPR). The nitrogen-containing condensed aromaticcompound is preferably used for the electron-relay layer 307 because ofits stability.

Further, it is possible to use 7,7,8,8-tetracyanoquinodimethane(abbreviation: TCNQ), 1,4,5,8-naphthalenetetracarboxylic dianhydride(abbreviation: NTCDA), perfluoropentacene, copperhexadecafluorophthalocyanine (abbreviation: F₁₆CuPc),N,H′-bis(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctyl)-1,4,5,8-naphthalenetetracarboxylicdiimide (abbreviation: NTCDI-C8F),3′,4′-dibutyl-5,5″-bis(dicyanomethylene)-5,5″-dihydro-2,2′:5′,2″-terthiophene(abbreviation: DCMT), or a methanofullerene (e.g., [6,6]-phenyl C₆₁butyric acid methyl ester).

The electron-relay layer 307 may further contain any of theabove-described donor substances. When the donor substance is containedin the electron-relay layer 307, electrons can be transferred easily andthe light-emitting element can be driven at a lower voltage.

The LUMO levels of the substance having the high electron-transportproperty and the donor substance are preferably −5.0 eV to −3.0 eV,i.e., between the LUMO level of the acceptor substance contained in thecharge-generation region 308 and the LUMO level of the substance havingthe high electron-transport property contained in the electron-transportlayer 304 (or the LUMO level of the EL layer 203 in contact with theelectron-relay layer 307 or with the electron-injection buffer layer 306therebetween). When a donor substance is contained in the electron-relaylayer 307, as the substance having the high electron-transport property,a substance having a LUMO level higher than the acceptor level of theacceptor substance contained in the charge-generation region 308 can beused.

The above-described layers included in the EL layer 203 and theintermediate layer 207 can be formed separately by any of the followingmethods: an evaporation method (including a vacuum evaporation method),a transfer method, a printing method, an inkjet method, a coatingmethod, and the like.

By use of the light-emitting element described in this embodiment, apassive matrix light-emitting device or an active matrix light-emittingdevice in which driving of the light-emitting element is controlled by atransistor can be manufactured. Furthermore, the light-emitting devicecan be applied to an electronic device, a lighting device, or the like.

This embodiment can be combined with any of other embodiments asappropriate.

Embodiment 2

In this embodiment, a light-emitting element in one embodiment of thepresent invention will be described with reference to FIGS. 2A to 2C.

A light-emitting element illustrated in FIG. 2A includes an EL layer 203between a first electrode 201 and a second electrode 205. The EL layer203 includes a light-emitting layer 213.

In the light-emitting element illustrated in FIG. 2A, the light-emittinglayer 213 contains a first organic compound 221, a second organiccompound 222, and a phosphorescent compound 223. The first organiccompound 221 is represented by the general formula (G0) shown inEmbodiment 1 and has a molecular weight greater than or equal to 500 andless than or equal to 2000. The second organic compound 222 is acompound having an electron-transport property.

The phosphorescent compound 223 is a guest material in thelight-emitting layer 213. In this embodiment, one of the first organiccompound 221 and the second organic compound 222, the content of whichis higher than that of the other in the light-emitting layer 213, is thehost material in the light-emitting layer 213.

Note that it is preferable that a triplet excitation energy level (T₁level) of each of the first organic compound 221 and the second organiccompound 222 be higher than that of the phosphorescent compound 223.This is because, when the T₁ level of the first organic compound 221 (orthe second organic compound 222) is lower than that of thephosphorescent compound 223, the triplet excitation energy of thephosphorescent compound 223, which is to contribute to light emission,is quenched by the first organic compound 221 (or the second organiccompound 222) and accordingly the emission efficiency is decreased.

Here, for improvement in efficiency of energy transfer from a hostmaterial to a guest material, Forster mechanism (dipole-dipoleinteraction) and Dexter mechanism (electron exchange interaction), whichare known as mechanisms of energy transfer between molecules, areconsidered. According to the mechanisms, it is preferable that anemission spectrum of a host molecule (a fluorescence spectrum in energytransfer from a singlet excited state, and a phosphorescence spectrum inenergy transfer from a triplet excited state) largely overlap with anabsorption spectrum of a guest molecule (specifically, a spectrum in anabsorption band on the longest wavelength (lowest energy) side).

However, in the case of using a phosphorescent compound as a guestmaterial, it is difficult to obtain an overlap between a fluorescencespectrum of a host material and an absorption spectrum in an absorptionband on the longest wavelength (lowest energy) side of the guestmaterial. The reason for this is as follows: if the fluorescencespectrum of the host material overlaps with the absorption spectrum inthe absorption band on the longest wavelength (lowest energy) side ofthe guest material, since a phosphorescence spectrum of the hostmaterial is located on a longer wavelength (lower energy) side than thefluorescence spectrum, the T₁ level of the host material becomes lowerthan the T₁ level of the phosphorescent compound and the above-describedproblem of quenching occurs; yet, when the host material is designed sothat the T₁ level of the host material is higher than the T₁ level ofthe phosphorescent compound to avoid the problem of quenching, thefluorescence spectrum of the host material is shifted to the shorterwavelength (higher energy) side, and thus the fluorescence spectrum doesnot have any overlap with the absorption spectrum in the absorption bandon the longest wavelength (lowest energy) side of the guest material.For that reason, in general, it is difficult to obtain an overlapbetween a fluorescence spectrum of the host material and an absorptionspectrum in an absorption band on the longest wavelength (lowest energy)side of the guest material so as to maximize energy transfer from asinglet excited state of the host material.

Thus, in this embodiment, a combination of the first organic compound221 and the second organic compound 222 forms an exciplex.

The exciplex will be described with reference to FIGS. 2B and 2C.

FIG. 2B is a schematic view showing the concept of an exciplex; afluorescence spectrum of the first organic compound 221 (or the secondorganic compound 222), a phosphorescence spectrum of the first organiccompound 221 (or the second organic compound 222), an absorptionspectrum of the phosphorescent compound 223, and an emission spectrum ofthe exciplex are shown.

For example, in the light-emitting layer 213, the fluorescence spectrumof the first organic compound 221 and the fluorescence spectrum of thesecond organic compound 222 are converted into an emission spectrum ofan exciplex which is located on the longer wavelength side. Moreover,when the first organic compound 221 and the second organic compound 222are selected so that the emission spectrum of the exciplex largelyoverlaps with the absorption spectrum of the phosphorescent compound 223(guest material), energy transfer from a singlet excited state can bemaximized (see FIG. 2B).

Note that also in the case of a triplet excited state, energy transferfrom the exciplex, not the host material, is considered to occur.

Thus, since the emission wavelength of the formed exciplex is longerthan the emission wavelength (fluorescence wavelength) of each of thefirst organic compound 221 and the second organic compound 222, thefluorescence spectrum of the first organic compound 221 or thefluorescence spectrum of the second organic compound 222 can become anemission spectrum located on the longer wavelength side.

Furthermore, the exciplex is considered to have an extremely smalldifference between singlet excited energy and triplet excited energy. Inother words, the emission spectrum of the exciplex from the single stateand the emission spectrum thereof from the triplet state are highlyclose to each other. Accordingly, in the case where a design isimplemented such that the emission spectrum of the exciplex (generallythe emission spectrum of the exciplex from the singlet state) overlapswith the absorption band of the phosphorescent compound 223 (guestmaterial) which is located on the longest wavelength side as describedabove, the emission spectrum of the exciplex from the triplet state(which is not observed at room temperature and not observed even at lowtemperature in many cases) also overlaps with the absorption band of thephosphorescent compound 223 (guest material) which is located on thelongest wavelength side. In other words, the efficiency of the energytransfer from the triplet excited state as well as the efficiency of theenergy transfer from the singlet excited state can be increased, and asa result, light emission can be efficiently obtained from both thesinglet and triplet excited states.

In the above manner, the light-emitting element in one embodiment of thepresent invention transfers energy by utilizing an overlap between theemission spectrum of the exciplex formed in the light-emitting layer 213and the absorption spectrum of the phosphorescent compound 223 (guestmaterial) and thus has high energy transfer efficiency.

In addition, the exciplex exists only in an excited state and thus hasno ground state capable of absorbing energy. Therefore, a phenomenon inwhich the phosphorescent compound 223 (guest material) is deactivated byenergy transfer from the phosphorescent compound 223 (guest material) inthe singlet excited state and triplet excited state to the exciplexbefore light emission (i.e., emission efficiency is lowered) is notconsidered to occur in principle.

Note that the above-described exciplex is formed by an interactionbetween dissimilar molecules in excited states. The exciplex isgenerally known to be easily formed between a material having arelatively deep LUMO level and a material having a relatively shallowhighest occupied molecular orbital (HOMO) level.

Here, concepts of the energy levels of the first organic compound 221,the second organic compound 222, and the exciplex are described withreference to FIG. 2C. Note that FIG. 2C schematically illustrates theenergy levels of the first organic compound 221, the second organiccompound 222, and the exciplex.

The HOMO levels and the LUMO levels of the first organic compound 221and the second organic compound 222 are different from each other.Specifically, the energy levels vary in the following order: the HOMOlevel of the second organic compound 222<the HOMO level of the firstorganic compound 221<the LUMO level of the second organic compound222<the LUMO level of the first organic compound 221. When the exciplexis formed by these two organic compounds, the LUMO level and the HOMOlevel of the exciplex originate from the second organic compound 222 andthe first organic compound 221, respectively (see FIG. 2C).

The emission wavelength of the exciplex depends on a difference inenergy between the HOMO level and the LUMO level. As a general tendency,when the energy difference is large, the emission wavelength is short,and when the energy difference is small, the emission wavelength islong.

Therefore, the energy difference of the exciplex is smaller than theenergy difference of the first organic compound 221 and the energydifference of the second organic compound 222. In other words, theemission wavelength of the exciplex is longer than the emissionwavelengths of the first organic compound 221 and the second organiccompound 222.

The process of the exciplex formation in one embodiment of the presentinvention can be either of the following two processes.

One process of the exciplex formation is that an exciplex is formed fromthe first organic compound 221 and the second organic compound 222having carriers (cation or anion).

In general, when an electron and a hole are recombined in a hostmaterial, excitation energy is transferred from the host material in anexcited state to a guest material, whereby the guest material is broughtinto an excited state to emit light. Before the excitation energy istransferred from the host material to the guest material, the hostmaterial itself emits light or the excitation energy turns into thermalenergy, which leads to partial deactivation of the excitation energy.

However, in one embodiment of the present invention, an exciplex isformed from the first organic compound 221 and the second organiccompound 222 having carriers (cation or anion); therefore, formation ofsinglet excitons of the first organic compound 221 and the secondorganic compound 222 can be suppressed. In other words, there can be aprocess where an exciplex is directly formed without formation of asinglet exciton. Thus, deactivation of the singlet excitation energy canbe inhibited. Accordingly, a light-emitting element having a longlifetime can be obtained.

For example, in the case where the first organic compound 221 is ahole-trapping compound having the property of easily capturing holes(carrier) (having a shallow HOMO level) among hole-transport materialsand the second organic compound 222 is an electron-trapping compoundhaving the property of easily capturing electrons (carrier) (having adeep LUMO level) among electron-transport materials, an exciplex isformed directly from a cation of the first organic compound 221 and ananion of the second organic compound 222. An exciplex formed throughsuch a process is particularly referred to as an electroplex.

A light-emitting element having high emission efficiency can be obtainedby suppressing the generation of the singlet excited states of the firstorganic compound 221 and the second organic compound 222 andtransferring energy from an electroplex to the phosphorescent compound223 (guest material), in the above-described manner. Note that in thiscase, the generation of the triplet excited states of the first organiccompound 221 and the second organic compound 222 is similarly suppressedand an exciplex is directly formed; therefore, energy transfer isconsidered to occur from the exciplex to the phosphorescent compound 223(guest material).

The other process of the exciplex formation is an elementary processwhere one of the first organic compound 221 and the second organiccompound 222 forms a singlet exciton and then interacts with the otherin the ground state to form an exciplex. Unlike an electroplex, asinglet excited state of the first organic compound 221 or the secondorganic compound 222 is temporarily generated in this case, but this israpidly converted into an exciplex, and thus, deactivation of singletexcitation energy, reaction from a singlet excited state, and the likecan be inhibited. This makes it possible to inhibit deactivation ofexcitation energy of the first organic compound 221 or the secondorganic compound 222; thus, a light-emitting element having a longlifetime can be obtained. Note that in this case, it is considered thatthe triplet excited state of the first organic compound 221 or thesecond organic compound 222 is similarly rapidly converted into anexciplex and energy is transferred from the exciplex to thephosphorescent compound 223 (guest material).

Note that, in the case where the first organic compound 221 is ahole-trapping compound, the second organic compound 222 is anelectron-trapping compound, and the difference between the HOMO levelsand the difference between the LUMO levels of these compounds are large(specifically, 0.3 eV or more), holes are selectively injected into thefirst organic compound 221 and electrons are selectively injected intothe second organic compound 222. In this case, it is thought that theprocess where an electroplex is formed takes precedence over the processwhere an exciplex is formed through a singlet exciton.

In general, energy transfer from the singlet excited state or tripletexcited state of a host material to a phosphorescent compound isconsidered. On the other hand, one embodiment of the present inventiongreatly differs from a conventional technique in that an exciplex of ahost material and another material is formed first and energy transferfrom the exciplex is used. In addition, this difference providesunprecedentedly high emission efficiency.

Note that in general, the use of an exciplex for a light-emitting layerof a light-emitting element has a value such as being capable ofcontrolling the emission color, but usually causes a significantdecrease in emission efficiency. Therefore, the use of an exciplex hasbeen considered unsuitable for obtaining a highly efficientlight-emitting element. However, the use of an exciplex as a medium forenergy transfer enables, on the contrary, emission efficiency to bemaximized as shown in one embodiment of the present invention. Thistechnical idea conflicts with the conventional fixed idea.

To make the emission spectrum of the exciplex and the absorptionspectrum of the phosphorescent compound 223 (guest material)sufficiently overlap each other, the difference between the energy of apeak of the emission spectrum and the energy of a peak of the absorptionband on the lowest energy side in the absorption spectrum is preferably0.3 eV or less. The difference is more preferably 0.2 eV or less, evenmore preferably 0.1 eV or less.

In the light-emitting element in one embodiment of the presentinvention, it is also preferable that the excitation energy of theexciplex be sufficiently transferred to the phosphorescent compound 223(guest material), and that light emission from the exciplex be notsubstantially observed. Therefore, energy is preferably transferred tothe phosphorescent compound 223 (guest material) through the exciplex sothat the phosphorescent compound 223 emits phosphorescence.

In the case where a phosphorescent compound is used as the host materialin the light-emitting element in one embodiment of the presentinvention, the host material itself is likely to emit light and unlikelyto allow energy to be transferred to the guest material. In this case,it is favorable if the phosphorescent compound used as the host materialcould emit light efficiently, but it is difficult to achieve highemission efficiency because the host material causes the problem ofconcentration quenching. Therefore, the case where at least one of thefirst organic compound 221 and the second organic compound 222 is afluorescent compound (i.e., a compound which is likely to undergo lightemission or thermal deactivation from the singlet excited state) iseffective. Therefore, it is preferable that at least one of the firstorganic compound 221 and the second organic compound 222 be afluorescent compound.

In the light-emitting element described in this embodiment, energytransfer efficiency can be improved owing to energy transfer utilizingan overlap between an emission spectrum of an exciplex and an absorptionspectrum of a phosphorescent compound (guest material); accordingly, thelight-emitting element can achieve high emission efficiency.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 3

In this embodiment, a light-emitting device in one embodiment of thepresent invention will be described with reference to FIGS. 3A and 3B.FIG. 3A is a plan view of a light-emitting device in one embodiment ofthe present invention, and FIG. 3B is a cross-sectional view taken alongdashed-dotted line A-B in FIG. 3A.

In the light-emitting device of this embodiment, a light-emittingelement 403 (a first electrode 421, an EL layer 423, and a secondelectrode 425) is provided in a space 415 surrounded by a supportsubstrate 401, a sealing substrate 405, and a sealing material 407. Thelight-emitting element 403 has a bottom-emission structure;specifically, the first electrode 421 which transmits visible light isprovided over the support substrate 401, the EL layer 423 is providedover the first electrode 421, and the second electrode 425 whichreflects visible light is provided over the EL layer 423.

As the light-emitting element 403 of this embodiment, the light-emittingelement in one embodiment of the present invention is used. Since thelight-emitting element in one embodiment of the present invention has along lifetime, a light-emitting device having high reliability can beobtained. In addition, since the light-emitting element in oneembodiment of the present invention exhibits high emission efficiency ina high luminance region, a light-emitting device with high emissionefficiency can be obtained.

A first terminal 409 a is electrically connected to an auxiliary wiring417 and the first electrode 421. An insulating layer 419 is providedover the first electrode 421 in a region which overlaps with theauxiliary wiring 417. The first terminal 409 a is electrically insulatedfrom the second electrode 425 by the insulating layer 419. A secondterminal 409 b is electrically connected to the second electrode 425.Note that although the first electrode 421 is formed over the auxiliarywiring 417 in this embodiment, the auxiliary wiring 417 may be formedover the first electrode 421.

Since the organic EL element emits light in a region having a refractiveindex higher than that of the atmosphere, total reflection may occurinside the organic EL element or at the interface between the organic ELelement and the atmosphere under a certain condition when light isextracted to the atmosphere, which results in a light extractionefficiency of the organic EL element lower than 100%.

Therefore, a light extraction structure 411 a is preferably provided atthe interface between the support substrate 401 and the atmosphere. Therefractive index of the support substrate 401 is higher than that of theatmosphere. Therefore, when provided at the interface between thesupport substrate 401 and the atmosphere, the light extraction structure411 a can reduce light which cannot be extracted to the atmosphere dueto total reflection, resulting in an increase in the light extractionefficiency of the light-emitting device.

In addition, a light extraction structure 411 b is preferably providedat the interface between the light-emitting element 403 and the supportsubstrate 401.

However, unevenness of the first electrode 421 might lead to generationof leakage current in the EL layer 423 formed over the first electrode421. Therefore, in this embodiment, a planarization layer 413 having arefractive index higher than or equal to that of the EL layer 423 isprovided in contact with the light extraction structure 411 b.Accordingly, the first electrode 421 can be a flat film, and generationof leakage current in the EL layer 423 due to the unevenness of thefirst electrode 421 can be prevented. Further, because of the lightextraction structure 411 b at the interface between the planarizationlayer 413 and the support substrate 401, light which cannot be extractedto the atmosphere due to total reflection can be reduced, so that thelight extraction efficiency of the light-emitting device can beincreased.

The present invention is not limited to the structure in which thesupport substrate 401, the light extraction structure 411 a, and thelight extraction structure 411 b are different components as in FIG. 3B.Two or all of these may be formed as one component. Further, theplanarization layer 413 is not necessarily provided in the case wherethe light extraction structure 411 b does not cause the first electrode421 to have surface unevenness (e.g., in the case where the lightextraction structure 411 b does not have surface unevenness), forexample.

The present invention is not limited to the structure in which thelight-emitting device is octagonal as illustrated in FIG. 3A. Thelight-emitting device may have any other polygonal shape or a shapehaving a curved portion. In particular, the light-emitting devicepreferably has a triangular, quadrilateral, or hexagonal shape or thelike so that a plurality of light-emitting devices can be provided in alimited area without a redundant space or so that a light-emittingdevice can be formed using a limited substrate area efficiently.Further, the number of light-emitting elements included in thelight-emitting device is not limited to one and may be more than one.

The shape of the unevenness of the light extraction structure 411 a andthe light extraction structure 411 b does not necessarily haveregularity. When the shape of the unevenness is periodic, the unevennessfunctions as a diffraction grating depending on the size of theunevenness, so that an interference effect is increased and light with acertain wavelength is easily extracted to the atmosphere. Therefore, itis preferable that the shape of the unevenness be not periodic.

There is no particular limitation on the bottom shape of the unevenness;for example, the shape may be a polygon such a triangle or a quadrangle,a circle, or the like. When the bottom shape of the unevenness hasregularity, the unevenness is preferably provided so that gaps are notformed between adjacent portions of the unevenness. A regular hexagoncan be given as an example of a preferable bottom shape.

There is no particular limitation on the shape of the unevenness; forexample, a hemisphere or a shape with a vertex such as a circular cone,a pyramid (e.g., a triangular pyramid or a quadrangular pyramid), or anumbrella shape can be used.

It is particularly preferable that the size or height of the unevennessbe greater than or equal to 1 μm, in which case the influence ofinterference of light can be reduced.

The light extraction structure 411 a and the light extraction structure411 b can be directly manufactured on the support substrate 401. Forexample, the light extraction structure 411 a and the light extractionstructure 411 b can be formed using any of the following methods asappropriate: an etching method, a sand blasting method, a microblastprocessing method, a frost processing method, a droplet dischargemethod, a printing method (screen printing or offset printing by which apattern is formed), a coating method such as a spin coating method, adipping method, a dispenser method, an imprint method, a nanoimprintmethod, and the like.

As a material of the light extraction structure 411 a and the lightextraction structure 411 b, a resin can be used, for example.Alternatively, for the light extraction structure 411 a and the lightextraction structure 411 b, a hemispherical lens, a micro lens array, afilm provided with an uneven surface structure, a light diffusing film,or the like can be used. For example, the light extraction structure 411a and the light extraction structure 411 b can be formed by attachingthe lens or film to the support substrate 401 with an adhesive or thelike which has substantially the same refractive index as the supportsubstrate 401 or the lens or film.

The surface of the planarization layer 413 which is in contact with thefirst electrode 421 is flatter than the surface of the planarizationlayer 413 which is in contact with the light extraction structure 411 b.Therefore, the first electrode 421 can be a flat film. As a result,generation of leakage current in the EL layer 423 due to unevenness ofthe first electrode 421 can be suppressed. As a material of theplanarization layer 413, glass, resin, or the like having a highrefractive index can be used. The planarization layer 413 has alight-transmitting property.

This embodiment can be combined with any of other embodiments asappropriate.

Embodiment 4

In this embodiment, a light-emitting device in one embodiment of thepresent invention will be described with reference to FIGS. 4A and 4B.FIG. 4A is a plan view of a light-emitting device in one embodiment ofthe present invention, and FIG. 4B is a cross-sectional view taken alongdashed-dotted line C-D in FIG. 4A.

An active matrix light-emitting device in this embodiment includes, overa support substrate 501, a light-emitting portion 551, a driver circuitportion 552 (gate side driver circuit portion), a driver circuit portion553 (source side driver circuit portion), and a sealing material 507.The light-emitting portion 551 and the driver circuit portions 552 and553 are sealed in a space 515 surrounded by the support substrate 501,the sealing substrate 505, and the sealing material 507.

The light-emitting portion 551 illustrated in FIG. 4B includes aplurality of light-emitting units each including a switching transistor541 a, a current control transistor 541 b, and a second electrode 525electrically connected to a wiring (a source electrode or a drainelectrode) of the transistor 541 b.

A light-emitting element 503 has a top-emission structure and includes afirst electrode 521 which transmits visible light, an EL layer 523, andthe second electrode 525 which reflects visible light. Further, apartition 519 is formed so as to cover an end portion of the secondelectrode 525.

As the light-emitting element 503 of this embodiment, the light-emittingelement in one embodiment of the present invention is used. Since thelight-emitting element in one embodiment of the present invention has along lifetime, a light-emitting device having high reliability can beobtained. In addition, since the light-emitting element in oneembodiment of the present invention exhibits high emission efficiency ina high luminance region, a light-emitting device with high emissionefficiency can be obtained.

Over the support substrate 501, a lead wiring 517 for connecting anexternal input terminal through which a signal (e.g., a video signal, aclock signal, a start signal, or a reset signal) or a potential from theoutside is transmitted to the driver circuit portion 552 or 553 isprovided. Here, an example is described in which a flexible printedcircuit (FPC) 509 is provided as the external input terminal. Note thata printed wiring board (PWB) may be attached to the FPC 509. In thisspecification, the light-emitting device includes in its category thelight-emitting device itself and the light-emitting device provided withthe FPC or the PWB.

The driver circuit portions 552 and 553 include a plurality oftransistors. FIG. 4B illustrates an example in which the driver circuitportion 552 has a CMOS circuit which is a combination of an n-channeltransistor 542 and a p-channel transistor 543. A circuit included in thedriver circuit portion can be formed with various types of circuits suchas a CMOS circuit, a PMOS circuit, or an NMOS circuit. The presentinvention is not limited to a driver-integrated type described in thisembodiment in which the driver circuit is formed over the substrate overwhich the light-emitting portion is formed. The driver circuit can beformed over a substrate that is different from the substrate over whichthe light-emitting portion is formed.

To prevent an increase in the number of manufacturing steps, the leadwiring 517 is preferably formed using the same material and the samestep(s) as those of the electrode or the wiring in the light-emittingportion or the driver circuit portion.

Described in this embodiment is an example in which the lead wiring 517is formed using the same material and the same step(s) as those of thesource electrodes and the drain electrodes of the transistors includedin the light-emitting portion 551 and the driver circuit portion 552.

In FIG. 4B, the sealing material 507 is in contact with a firstinsulating layer 511 over the lead wiring 517. The adhesion of thesealing material 507 to metal is low in some cases. Therefore, thesealing material 507 is preferably in contact with an inorganicinsulating film over the lead wiring 517. Such a structure enables alight-emitting device to have high sealing capability, high adhesion,and high reliability. Examples of the inorganic insulating film includeoxide films of metals and semiconductors, nitride films of metals andsemiconductors, and oxynitride films of metals and semiconductors, andspecifically, a silicon oxide film, a silicon nitride film, a siliconoxynitride film, a silicon nitride oxide film, an aluminum oxide film, atitanium oxide film, and the like.

The first insulating layer 511 has an effect of preventing diffusion ofimpurities into a semiconductor included in the transistor. As thesecond insulating layer 513, an insulating film having a planarizationfunction is preferably selected in order to reduce surface unevennessdue to the transistor.

There is no particular limitation on the structure of the transistorused in the light-emitting device of one embodiment of the presentinvention. A top-gate transistor may be used, or a bottom-gatetransistor such as an inverted staggered transistor may be used. Thetransistor may be a channel-etched transistor or a channel-protectivetransistor. In addition, there is no particular limitation on a materialused for the transistor.

A semiconductor layer can be formed using silicon or an oxidesemiconductor. As silicon, single crystal silicon, polycrystallinesilicon, or the like can be used as appropriate. As an oxidesemiconductor, an In—Ga—Zn-based metal oxide or the like can be used asappropriate. Note that the transistor is preferably formed using anoxide semiconductor which is an In—Ga—Zn-based metal oxide for asemiconductor layer so as to have low off-state current, in which casean off-state leakage current of the light-emitting element can bereduced.

The sealing substrate 505 is provided with a color filter 533 which is acoloring layer overlapping with the light-emitting element 503 (itslight-emitting region). The color filter 533 is provided to control thecolor of light emitted from the light-emitting element 503. For example,in a full-color display device using white light-emitting elements, aplurality of light-emitting units provided with color filters ofdifferent colors are used. In that case, three colors, red (R), green(G), and blue (B), may be used, or four colors, red (R), green (G), blue(B), and yellow (Y), may be used.

Further, a black matrix 531 is provided between adjacent color filters533 (so as to overlap with the partition 519). The black matrix 531shields a light-emitting unit from light emitted from the light-emittingelements 503 in adjacent light-emitting units and prevents color mixturebetween the adjacent light-emitting units. When the color filter 533 isprovided so that its end portion overlaps with the black matrix 531,light leakage can be reduced. The black matrix 531 can be formed using amaterial that blocks light emitted from the light-emitting element 503,for example, a material such as a metal or a resin. Note that the blackmatrix 531 may be provided also in a region overlapping with the drivercircuit portion 552 or the like besides the light-emitting portion 551.

Further, an overcoat layer 535 is formed so as to cover the color filter533 and the black matrix 531. For the overcoat layer 535, a materialwhich transmits light emitted from the light-emitting element 503 isused, and an inorganic insulating film or an organic insulating film canbe used, for example. The overcoat layer 535 is not necessarily providedwhen not needed.

A structure of the present invention is not limited to thelight-emitting device using a color filter method, which is described asan example in this embodiment. For example, a separate coloring methodor a color conversion method may be used.

This embodiment can be combined with any of other embodiments asappropriate.

Embodiment 5

In this embodiment, examples of electronic devices and lighting devicesto which the light-emitting device in one embodiment of the presentinvention is applied will be described with reference to FIGS. 5A to 5Eand FIGS. 6A and 6B.

Electronic devices of this embodiment each include the light-emittingdevice of one embodiment of the present invention in a display portion.Lighting devices of this embodiment each include the light-emittingdevice of one embodiment of the present invention in a light-emittingportion (lighting portion). Highly reliable electronic devices andhighly reliable lighting devices can be provided by adopting thelight-emitting device of one embodiment of the present invention. Inaddition, electronic devices and lighting devices having high emissionefficiency can be provided by adopting the light-emitting device of oneembodiment of the present invention.

Examples of electronic devices to which the light-emitting device isapplied are television devices (also referred to as TV or televisionreceivers), monitors for computers and the like, cameras such as digitalcameras and digital video cameras, digital photo frames, cellular phones(also referred to as portable telephone devices), portable gamemachines, portable information terminals, audio playback devices, largegame machines such as pin-ball machines, and the like. Specific examplesof these electronic devices and lighting devices are illustrated inFIGS. 5A to 5E and FIGS. 6A and 6B.

FIG. 5A illustrates an example of a television device. In a televisiondevice 7100, a display portion 7102 is incorporated in a housing 7101.The display portion 7102 is capable of displaying images. Thelight-emitting device in one embodiment of the present invention can beused for the display portion 7102. In addition, here, the housing 7101is supported by a stand 7103.

The television device 7100 can be operated with an operation switchprovided in the housing 7101 or a separate remote controller 7111. Withoperation keys of the remote controller 7111, channels and volume can becontrolled and images displayed on the display portion 7102 can becontrolled. The remote controller 7111 may be provided with a displayportion for displaying data output from the remote controller 7111.

Note that the television device 7100 is provided with a receiver, amodem, and the like. With the use of the receiver, general televisionbroadcasting can be received. Moreover, when the television device isconnected to a communication network with or without wires via themodem, one-way (from a sender to a receiver) or two-way (between asender and a receiver or between receivers) information communicationcan be performed.

FIG. 5B illustrates an example of a computer. A computer 7200 includes amain body 7201, a housing 7202, a display portion 7203, a keyboard 7204,an external connection port 7205, a pointing device 7206, and the like.Note that this computer is manufactured by using the light-emittingdevice of one embodiment of the present invention for the displayportion 7203.

FIG. 5C illustrates an example of a portable game machine. A portablegame machine 7300 has two housings, a housing 7301 a and a housing 7301b, which are connected with a joint portion 7302 so that the portablegame machine can be opened or closed. The housing 7301 a incorporates adisplay portion 7303 a, and the housing 7301 b incorporates a displayportion 7303 b. In addition, the portable game machine illustrated inFIG. 5C includes a speaker portion 7304, a recording medium insertionportion 7305, an operation key 7306, a connection terminal 7307, asensor 7308 (a sensor having a function of measuring or sensing force,displacement, position, speed, acceleration, angular velocity,rotational frequency, distance, light, liquid, magnetism, temperature,chemical substance, sound, time, hardness, electric field, electriccurrent, voltage, electric power, radiation, flow rate, humidity,gradient, oscillation, odor, or infrared rays), an LED lamp, amicrophone, and the like. It is needless to say that the structure ofthe portable game machine is not limited to the above structure as longas the light-emitting device of one embodiment of the present inventionis used for at least either the display portion 7303 a or the displayportion 7303 b, or both, and may include other accessories asappropriate. The portable game machine illustrated in FIG. 5C has afunction of reading out a program or data stored in a recoding medium todisplay it on the display portion, and a function of sharing informationwith another portable game machine by wireless communication. Note thatfunctions of the portable game machine illustrated in FIG. 5C are notlimited to them, and the portable game machine can have variousfunctions.

FIG. 5D illustrates an example of a cellular phone. A cellular phone7400 is provided with a display portion 7402 incorporated in a housing7401, an operation button 7403, an external connection port 7404, aspeaker 7405, a microphone 7406, and the like. Note that the cellularphone 7400 is manufactured by using the light-emitting device of oneembodiment of the present invention for the display portion 7402.

When the display portion 7402 of the cellular phone 7400 illustrated inFIG. 5D is touched with a finger or the like, data can be input into thecellular phone. Further, operations such as making a call and creatingan e-mail can be performed by touching the display portion 7402 with afinger or the like.

There are mainly three screen modes of the display portion 7402. Thefirst mode is a display mode mainly for displaying an image. The secondmode is an input mode mainly for inputting information such ascharacters. The third mode is a display-and-input mode in which twomodes of the display mode and the input mode are combined.

For example, in the case of making a call or creating e-mail, acharacter input mode mainly for inputting characters is selected for thedisplay portion 7402 so that characters displayed on the screen can beinput.

When a sensing device including a sensor such as a gyroscope sensor oran acceleration sensor for detecting inclination is provided inside thecellular phone 7400, display on the screen of the display portion 7402can be automatically changed in direction by determining the orientationof the cellular phone 7400 (whether the cellular phone 7400 is placedhorizontally or vertically for a landscape mode or a portrait mode).

The screen modes are changed by touch on the display portion 7402 oroperation with the operation button 7403 of the housing 7401. The screenmodes can be switched depending on the kind of images displayed on thedisplay portion 7402. For example, when a signal of an image displayedon the display portion is a signal of moving image data, the screen modeis switched to the display mode. When the signal is a signal of textdata, the screen mode is switched to the input mode.

Moreover, in the input mode, if a signal detected by an optical sensorin the display portion 7402 is detected and the input by touch on thedisplay portion 7402 is not performed for a certain period, the screenmode may be controlled so as to be changed from the input mode to thedisplay mode.

The display portion 7402 may function as an image sensor. For example,an image of a palm print, a fingerprint, or the like is taken by thedisplay portion 7402 while in touch with the palm or the finger, wherebypersonal authentication can be performed. Further, when a backlight or asensing light source which emits near-infrared light is provided in thedisplay portion, an image of a finger vein, a palm vein, or the like canbe taken.

FIG. 5E illustrates an example of a fordable tablet terminal (in an openstate). A tablet terminal 7500 includes a housing 7501 a, a housing 7501b, a display portion 7502 a, and a display portion 7502 b. The housing7501 a and the housing 7501 b are connected by a hinge 7503 and can beopened and closed using the hinge 7503 as an axis. The housing 7501 aincludes a power switch 7504, operation keys 7505, a speaker 7506, andthe like. Note that the tablet terminal 7500 is manufactured by usingthe light-emitting device of one embodiment of the present invention foreither the display portion 7502 a or the display portion 7502 b, orboth.

Part of the display portion 7502 a or the display portion 7502 b can beused as a touch panel region, where data can be input by touchingdisplayed operation keys. For example, a keyboard can be displayed onthe entire region of the display portion 7502 a so that the displayportion 7502 a is used as a touch screen, and the display portion 7502 bcan be used as a display screen.

FIG. 6A illustrates a desk lamp, which includes a lighting portion 7601,a shade 7602, an adjustable arm 7603, a support 7604, a base 7605, and apower switch 7606. The desk lamp is manufactured by using thelight-emitting device of one embodiment of the present invention for thelighting portion 7601. Note that the lamp also includes ceiling lights,wall lights, and the like in its category.

FIG. 6B illustrates an example in which the light-emitting device of oneembodiment of the present invention is used for an indoor lamp 7701.Since the light-emitting device of one embodiment of the presentinvention can have a larger area, it can be used as a large-arealighting device. In addition, the light-emitting device can be used as aroll-type lamp 7702. As illustrated in FIG. 6B, a desk lamp 7703described with reference to FIG. 6A may be used in a room provided withthe indoor lamp 7701.

Example 1

In this example, a light-emitting element of one embodiment of thepresent invention will be described with reference to FIG. 7. Chemicalformulae of materials used in this example are shown below.

Methods for manufacturing a light-emitting element 1, a comparativelight-emitting element 2, and a comparative light-emitting element 3 ofthis example will be described below.

(Light-Emitting Element 1)

First, a film of indium tin oxide containing silicon oxide (ITSO) wasformed over a glass substrate 1100 by a sputtering method, so that afirst electrode 1101 was formed. The thickness thereof was 110 nm andthe electrode area was 2 mm×2 mm. Here, the first electrode 1101functions as an anode of the light-emitting element.

Next, as pretreatment for forming the light-emitting element over theglass substrate 1100, UV-ozone treatment was performed for 370 secondsafter washing of a surface of the substrate with water and baking thatwas performed at 200° C. for 1 hour.

After that, the glass substrate 1100 was transferred into a vacuumevaporation apparatus where the pressure had been reduced toapproximately 10⁻⁴ Pa, and was subjected to vacuum baking at 170° C. for30 minutes in a heating chamber of the vacuum evaporation apparatus, andthen the substrate was cooled down for about 30 minutes.

Then, the glass substrate 1100 over which the first electrode 1101 wasformed was fixed to a substrate holder provided in the vacuumevaporation apparatus so that the surface on which the first electrode1101 was formed faced downward. The pressure in the vacuum evaporationapparatus was reduced to about 10⁻⁴ Pa. After that, over the firstelectrode 1101, 4,4′,4″-(1,3,5-benzenetriyl)tri(dibenzothiophene)(abbreviation: DBT3P-II) and molybdenum(VI) oxide were deposited byco-evaporation by an evaporation method using resistance heating, sothat a hole-injection layer 1111 was formed. The thickness of thehole-injection layer 1111 was set to 40 nm, and the weight ratio ofDBT3P-II to molybdenum oxide was adjusted to 4:2 (=DBT3P-II:molybdenumoxide). Note that the co-evaporation method refers to an evaporationmethod in which evaporation is carried out from a plurality ofevaporation sources at the same time in one treatment chamber.

Next, a film of 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: BPAFLP) was formed to a thickness of 20 nm over thehole-injection layer 1111 to form a hole-transport layer 1112.

Further, a light-emitting layer 1113 was formed over the hole-transportlayer 1112 by co-evaporation of2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II),N-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine(abbreviation: PCBBiF), and(acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III)(abbreviation: [Ir(dppm)₂(acac)]). Here, the weight ratio of2mDBTBPDBq-II to PCBBiF and [Ir(dppm)₂(acac)] was adjusted to0.8:0.2:0.05 (=2mDBTBPDBq-II:PCBBiF:[Ir(dppm)₂(acac)]). The thickness ofthe light-emitting layer 1113 was set to 40 nm.

Then, an electron-transport layer 1114 was formed over thelight-emitting layer 1113 in such a way that a 15 nm thick film of2mDBTBPDBq-II was formed and a 15 nm thick film of bathophenanthroline(abbreviation: BPhen) was formed.

After that, over the electron-transport layer 1114, a film of lithiumfluoride (LiF) was formed by evaporation to a thickness of 1 nm to forman electron-injection layer 1115.

Lastly, aluminum was deposited by evaporation to a thickness of 200 nmto form a second electrode 1103 functioning as a cathode. Thus, thelight-emitting element 1 of this example was fabricated.

Note that in all the above evaporation steps, evaporation was performedby a resistance-heating method.

(Comparative Light-Emitting Element 2)

A light-emitting layer 1113 of the comparative light-emitting element 2was formed by co-evaporation of 2mDBTBPDBq-II,4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBNBB), and [Ir(dppm)₂(acac)]. Here, the weight ratio of2mDBTBPDBq-II to PCBNBB and [Ir(dppm)₂(acac)] was adjusted to0.8:0.2:0.05 (=2mDBTBPDBq-II:PCBNBB:[Ir(dppm)₂(acac)]). The thickness ofthe light-emitting layer 1113 was set to 40 nm. Components other thanthe light-emitting layer 1113 were manufactured in a manner similar tothat of the light-emitting element 1.

(Comparative Light-Emitting Element 3)

A light-emitting layer 1113 of the comparative light-emitting element 3was formed by co-evaporation of 2mDBTBPDBq-II,N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-N-[4-(1-naphthyl)phenyl]-9H-fluoren-2-amine(abbreviation: PCBNBF), and [Ir(dppm)₂(acac)]. Here, the weight ratio of2mDBTBPDBq-II to PCBNBF and [Ir(dppm)₂(acac)] was adjusted to0.8:0.2:0.05 (=2mDBTBPDBq-II:PCBNBF:[Ir(dppm)₂(acac)]). The thickness ofthe light-emitting layer 1113 was set to 40 nm. Components other thanthe light-emitting layer 1113 were manufactured in a manner similar tothat of the light-emitting element 1.

Table 1 shows element structures of the light-emitting elements obtainedas described above in this example.

TABLE 1 hole- hole- electron- first injection transportelectron-transport injection second electrode layer layer light-emittinglayer layer layer electrode light-emitting ITSO DBT3P- BPAFLP2mDBTBPDBq- 2mDBTBPDBq-II BPhen LiF Al element 1 110 nm II:MoOx 20 nmII:PCBBiF:[Ir(dppm)₂(acac)] 15 nm 15 nm 1 nm 200 nm (=4:2)(=0.8:0.2:0.05) 40 nm 40 nm comparative 2mDBTBPDBq- light-emittingII:PCBNBB:[Ir(dppm)₂(acac)] element 2 (=0.8:0.2:0.05) 40 nm comparative2mDBTBPDBq- light-emitting II:PCBNBF:[Ir(dppm)₂(acac)] element 3(=0.8:0.2:0.05) 40 nm

The light-emitting element 1, the comparative light-emitting element 2,and the comparative light-emitting element 3 were each sealed using aglass substrate in a glove box containing a nitrogen atmosphere so asnot to be exposed to the air. Then, operational characteristics of theselight-emitting elements were measured. Note that the measurements werecarried out at room temperature (in an atmosphere kept at 25° C.).

FIG. 8 shows luminance-current efficiency characteristics of thelight-emitting elements of this example. In FIG. 8, the horizontal axisrepresents luminance (cd/m²), and the vertical axis represents currentefficiency (cd/A). FIG. 9 shows voltage-luminance characteristics. InFIG. 9, the horizontal axis represents voltage (V), and the verticalaxis represents luminance (cd/m²). FIG. 10 shows luminance-externalquantum efficiency characteristics. In FIG. 10, the horizontal axisrepresents luminance (cd/m²), and the vertical axis represents externalquantum efficiency (%). Table 2 shows the voltage (V), current density(mA/cm²), CIE chromaticity coordinates (x, y), current efficiency(cd/A), power efficiency (lm/W), and external quantum efficiency (%) ofeach of the light-emitting elements at a luminance of around 1000 cd/m².

TABLE 2 current current power external voltage density chromaticityluminance efficiency efficiency quantum (V) (mA/cm²) x y (cd/m²) (cd/A)(lm/W) efficiency (%) light-emitting 3.0 1.7 0.55 0.45 1200 67 70 26element 1 comparative 3.0 1.4 0.55 0.44 900 63 66 25 light-emittingelement 2 comparative 3.0 1.5 0.55 0.45 1000 66 69 25 light-emittingelement 3

As shown in Table 2, the CIE chromaticity coordinates of thelight-emitting element 1 at a luminance of 1200 cd/m² were (x, y)=(0.55,0.45). The CIE chromaticity coordinates of the comparativelight-emitting element 2 at a luminance of 900 cd/m² were (x, y)=(0.55,0.44). The CIE chromaticity coordinates of the comparativelight-emitting element 3 at a luminance of 1000 cd/m² were (x, y)=(0.55,0.45). It has been found that orange light emission originating from[Ir(dppm)₂(acac)] was obtained from the light-emitting elements of thisexample.

FIGS. 8 to 10 and Table 2 show that the light-emitting element 1, thecomparative light-emitting element 2, and the comparative light-emittingelement 3 can each be driven at low voltage and have high currentefficiency, high power efficiency, and high external quantum efficiency.

It has also been found that the current efficiency and the externalquantum efficiency in a high luminance region are higher in thelight-emitting element 1 than in the comparative light-emitting element2 and the comparative light-emitting element 3 (see the currentefficiency or the external quantum efficiency at a luminance of 1000cd/m² to 10000 cd/m² in FIG. 8 or FIG. 10). In the light-emittingelement 1, the light-emitting layer contains PCBBiF which has afluorenyl group, a biphenyl group, and a substituent including acarbazole skeleton. In the comparative light-emitting element 2, thelight-emitting layer contains PCBNBB which has two naphthyl groups and asubstituent including a carbazole skeleton. In the comparativelight-emitting element 3, the light-emitting layer contains PCBNBF whichhas a fluorenyl group, a naphthyl group, and a substituent including acarbazole skeleton. That is, a major difference between thelight-emitting element 1 and the comparative light-emitting element 2 or3 is whether or not the tertiary amine in the light-emitting layer has anaphthyl group. Since the tertiary amine used in the light-emittingelement 1 of one embodiment of the present invention has a biphenylamineskeleton and a fluorenylamine skeleton, it has a high hole-transportproperty and a high electron-blocking property. In addition, since thetertiary amine has a higher triplet excitation energy than an amineincluding a naphthalene skeleton or the like, it has an excellentexciton-blocking property. Therefore, electron leakage and excitondiffusion can be prevented even in a high luminance region, and thus alight-emitting element exhibiting high emission efficiency can beobtained.

Next, the light-emitting element 1, the comparative light-emittingelement 2, and the comparative light-emitting element 3 were subjectedto reliability tests. Results of the reliability tests are shown inFIGS. 11A and 11B. In FIGS. 11A and 11B, the vertical axis representsnormalized luminance (%) with an initial luminance of 100%, and thehorizontal axis represents driving time (h) of the elements. In thereliability tests, the light-emitting elements of this example weredriven at room temperature under the conditions where the initialluminance was set to 5000 cd/m² and the current density was constant.FIGS. 11A and 11B show that the light-emitting element 1 kept 95% of theinitial luminance after 460 hours elapsed, the comparativelight-emitting element 2 kept 92% of the initial luminance after 460hours elapsed, and the comparative light-emitting element 3 kept 94% ofthe initial luminance after 370 hours elapsed. The results of thereliability tests have revealed that the light-emitting element 1 has alonger lifetime than the comparative light-emitting element 2 and thecomparative light-emitting element 3.

As described above, in the light-emitting element 1 of one embodiment ofthe present invention, electron leakage and exciton diffusion can beprevented even in a high luminance region; thus, there are fewdeactivation pathways (non-radiative deactivation) other than transitionby light emission of the light-emitting substance (radiativedeactivation). Therefore, luminance degradation of the element can bereduced. In addition, such a light-emitting element with littledegradation can be obtained easily and stably with high reproducibility.

As described above, it has been found that a light-emitting elementexhibiting high emission efficiency in a high luminance region can beobtained in accordance with one embodiment of the present invention. Ithas also been found that a light-emitting element having a long lifetimecan be obtained in accordance with one embodiment of the presentinvention.

Example 2

In this example, a light-emitting element of one embodiment of thepresent invention will be described with reference to FIG. 7. Chemicalformulae of materials used in this example are shown below. Note thatthe chemical formulae of the materials already shown above are omitted.

Methods for manufacturing a light-emitting element 4 and a comparativelight-emitting element 5 of this example will be described below.

(Light-Emitting Element 4)

First, in a manner similar to that of the light-emitting element 1, afirst electrode 1101 and a hole-injection layer 1111 were formed over aglass substrate 1100.

Next, over the hole-injection layer 1111, a film of PCBBiF was formed toa thickness of 20 nm to form a hole-transport layer 1112.

Further, a light-emitting layer 1113 was formed over the hole-transportlayer 1112 by co-evaporation of 2mDBTBPDBq-II, PCBBiF, and(acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(tBuppm)₂(acac)]). Here, a 20 nm thick layer formedwith the weight ratio of 2mDBTBPDBq-II to PCBBiF and [Ir(tBuppm)₂(acac)]adjusted to 0.7:0.3:0.05 (=2mDBTBPDBq-II:PCBBiF:[Ir(tBuppm)₂(acac)]) anda 20 nm thick layer formed with the weight ratio of 2mDBTBPDBq-II toPCBBiF and [Ir(tBuppm)₂(acac)] adjusted to 0.8:0.2:0.05(=2mDBTBPDBq-II:PCBBiF:[Ir(tBuppm)₂(acac)]) were stacked.

Then, an electron-transport layer 1114 was formed over thelight-emitting layer 1113 in such a way that a 5 nm thick film of2mDBTBPDBq-II was formed and a 15 nm thick film of BPhen was formed.

Further, over the electron-transport layer 1114, a film of LiF wasformed by evaporation to a thickness of 1 nm to form anelectron-injection layer 1115.

Lastly, aluminum was deposited by evaporation to a thickness of 200 nmto form a second electrode 1103 functioning as a cathode. Thus, thelight-emitting element 4 of this example was fabricated.

Note that in all the above evaporation steps, evaporation was performedby a resistance-heating method.

(Comparative Light-Emitting Element 5)

A hole-transport layer 1112 of the comparative light-emitting element 5was formed by forming a film of PCBNBB to a thickness of 20 nm. Alight-emitting layer 1113 was formed by co-evaporation of 2mDBTBPDBq-II,PCBNBB, and [Ir(tBuppm)₂(acac)]. Here, a 20 nm thick layer formed withthe weight ratio of 2mDBTBPDBq-II to PCBNBB and [Ir(tBuppm)₂(acac)]adjusted to 0.7:0.3:0.05 (=2mDBTBPDBq-II:PCBNBB:[Ir(tBuppm)₂(acac)]) anda 20 nm thick layer formed with the weight ratio of 2mDBTBPDBq-II toPCBNBB and [Ir(tBuppm)₂(acac)] adjusted to 0.8:0.2:0.05(=2mDBTBPDBq-II:PCBNBB:[Ir(tBuppm)₂(acac)]) were stacked. Componentsother than the hole-transport layer 1112 and the light-emitting layer1113 were manufactured in a manner similar to that of the light-emittingelement 4.

Table 3 shows element structures of the light-emitting elements obtainedas described above in this example.

TABLE 3 hole- hole- electron- first injection transportelectron-transport injection second electrode layer layer light-emittinglayer layer layer electrode light-emitting ITSO DBT3P- PCBBiF2mDBTBPDBq- 2mDBTBPDBq-II BPhen LiF Al element 4 110 nm II:MoOx 20 nmII:PCBBiF:[Ir(tBuppm)₂(acac)] 5 nm 15 nm 1 nm 200 nm (=4:2)(=0.7:0.3:0.05) (=0.8:0.2:0.05) 20 nm 20 nm 20 nm comparative PCBNBB2mDBTBPDBq- light-emitting 20 nm II:PCBNBB:[Ir(tBuppm)₂(acac)] element 5(=0.7:0.3:0.05) (=0.8:0.2:0.05) 20 nm 20 nm

The light-emitting element 4 and the comparative light-emitting element5 were each sealed using a glass substrate in a glove box containing anitrogen atmosphere so as not to be exposed to the air. Then,operational characteristics of these light-emitting elements weremeasured. Note that the measurements were carried out at roomtemperature (in an atmosphere kept at 25° C.).

FIG. 12 shows luminance-current efficiency characteristics of thelight-emitting elements of this example. In FIG. 12, the horizontal axisrepresents luminance (cd/m²), and the vertical axis represents currentefficiency (cd/A). FIG. 13 shows voltage-luminance characteristics. InFIG. 13, the horizontal axis represents voltage (V), and the verticalaxis represents luminance (cd/m²). FIG. 14 shows luminance-powerefficiency characteristics. In FIG. 14, the horizontal axis representsluminance (cd/m²), and the vertical axis represents power efficiency(lm/W). FIG. 15 shows luminance-external quantum efficiencycharacteristics. In FIG. 15, the horizontal axis represents luminance(cd/m²), and the vertical axis represents external quantum efficiency(%). Table 4 shows the voltage (V), current density (mA/cm²), CIEchromaticity coordinates (x, y), current efficiency (cd/A), powerefficiency (lm/W), and external quantum efficiency (%) of thelight-emitting element 4 and the comparative light-emitting element 5 ata luminance of 900 cd/m².

TABLE 4 current current power external voltage density chromaticityluminance efficiency efficiency quantum (V) (mA/cm²) x y (cd/m²) (cd/A)(lm/W) efficiency (%) light-emitting 2.6 0.82 0.41 0.59 900 106 128 27element 4 comparative 2.7 0.94 0.40 0.59 900 92 108 24 light-emittingelement 5

As shown in Table 4, at a luminance of 900 cd/m², the CIE chromaticitycoordinates of the light-emitting element 4 were (x, y)=(0.41, 0.59),and the CIE chromaticity coordinates of the comparative light-emittingelement 5 were (x, y)=(0.40, 0.59). It has been found that green lightemission originating from [Ir(tBuppm)₂(acac)] was obtained from thelight-emitting element 4 and the comparative light-emitting element 5.

FIGS. 12 to 15 and Table 4 show that the light-emitting element 4 andthe comparative light-emitting element 5 can each be driven at extremelylow voltage. It has also been found that the light-emitting element 4has higher current efficiency, higher power efficiency, and higherexternal quantum efficiency than the comparative light-emitting element5 (see the current efficiency, the power efficiency, or the externalquantum efficiency at a luminance of 1000 cd/m² to 10000 cd/m² in FIG.12, FIG. 14, or FIG. 15).

In the light-emitting element 4, the light-emitting layer and thehole-transport layer contain PCBBiF which has a fluorenyl group, abiphenyl group, and a substituent including a carbazole skeleton. In thecomparative light-emitting element 5, the light-emitting layer and thehole-transport layer contain PCBNBB which has two naphthyl groups and asubstituent including a carbazole skeleton. That is, a major differencebetween the light-emitting element 4 and the comparative light-emittingelement 5 is whether or not the tertiary amine in the light-emittinglayer has a naphthyl group. Since the tertiary amine used in thelight-emitting element 4 of one embodiment of the present invention hasa biphenylamine skeleton and a fluorenylamine skeleton, it has a highhole-transport property and a high electron-blocking property. Inaddition, since the tertiary amine has a higher triplet excitationenergy than an amine including a naphthalene skeleton or the like, ithas an excellent exciton-blocking property. Therefore, electron leakageand exciton diffusion can be prevented even in a high luminance region,and thus a light-emitting element exhibiting high emission efficiencycan be obtained. The emission efficiency becomes higher when the samecompound as the tertiary amine contained in the light-emitting layer isused for the hole-transport layer. That is, although the drive voltagecan be decreased by the use of the same compound as the tertiary aminecontained in the light-emitting layer for the hole-transport layer as inthe light-emitting element 4 and the comparative light-emitting element5, the emission efficiency is lowered as in the comparativelight-emitting element 5 unless one embodiment of the present inventionis applied (unless the tertiary amine represented by the above generalformula (G0) is used).

As described above, it has been found that a light-emitting elementexhibiting high emission efficiency in a high luminance region can beobtained in accordance with one embodiment of the present invention. Ithas also been found that a light-emitting element which can be driven atlow voltage can be obtained in accordance with one embodiment of thepresent invention. It has been found that a light-emitting elementhaving particularly high emission efficiency can be obtained by the useof the first organic compound (the compound represented by the generalformula (G0) shown in Embodiment 1) for a hole-transport layer as wellas a light-emitting layer.

Next, the light-emitting element 4 and the comparative light-emittingelement 5 were subjected to reliability tests. Results of thereliability tests are shown in FIG. 16. In FIG. 16, the vertical axisrepresents normalized luminance (%) with an initial luminance of 100%,and the horizontal axis represents driving time (h) of the elements. Inthe reliability tests, the light-emitting elements of this example weredriven at room temperature under the conditions where the initialluminance was set to 5000 cd/m² and the current density was constant.FIG. 16 shows that the light-emitting element 4 kept 93% of the initialluminance after 160 hours elapsed and the comparative light-emittingelement 5 kept 89% of the initial luminance after 360 hours elapsed.

Example 3

In this example, a light-emitting element of one embodiment of thepresent invention will be described with reference to FIG. 7. Chemicalformulae of materials used in this example are shown below. Note thatthe chemical formulae of the materials already shown above are omitted.

Methods for manufacturing a light-emitting element 6 and alight-emitting element 7 of this example will be described below.

(Light-Emitting Element 6)

First, in a manner similar to that of the light-emitting element 1, afirst electrode 1101 and a hole-injection layer 1111 were formed over aglass substrate 1100.

Next, over the hole-injection layer 1111, a film ofN-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9′-spirobi[9H-fluoren]-2-amine(abbreviation: PCBBiSF) was formed to a thickness of 20 nm to form ahole-transport layer 1112.

Further, a light-emitting layer 1113 was formed over the hole-transportlayer 1112 by co-evaporation of 2mDBTBPDBq-II, PCBBiSF, and[Ir(dppm)₂(acac)]. Here, a 20 nm thick layer formed with the weightratio of 2mDBTBPDBq-II to PCBBiSF and [Ir(dppm)₂(acac)] adjusted to0.7:0.3:0.05 (=2mDBTBPDBq-II:PCBBiSF:[Ir(dppm)₂(acac)]) and a 20 nmthick layer formed with the weight ratio of 2mDBTBPDBq-II to PCBBiSF and[Ir(dppm)₂(acac)] adjusted to 0.8:0.2:0.05(=2mDBTBPDBq-II:PCBBiSF:[Ir(dppm)₂(acac)]) were stacked.

Then, an electron-transport layer 1114 was formed over thelight-emitting layer 1113 in such a way that a 20 nm thick film of2mDBTBPDBq-II was formed and a 20 nm thick film of BPhen was formed.

Further, over the electron-transport layer 1114, a film of LiF wasformed by evaporation to a thickness of 1 nm to form anelectron-injection layer 1115.

Lastly, aluminum was deposited by evaporation to a thickness of 200 nmto form a second electrode 1103 functioning as a cathode. Thus, thelight-emitting element 6 of this example was fabricated.

Note that in all the above evaporation steps, evaporation was performedby a resistance-heating method.

(Light-Emitting Element 7)

A hole-transport layer 1112 of the light-emitting element 7 was formedby forming a film of BPAFLP to a thickness of 20 nm. Components otherthan the hole-transport layer 1112 were manufactured in a manner similarto that of the light-emitting element 6.

Table 5 shows element structures of the light-emitting elements obtainedas described above in this example.

TABLE 5 hole- hole- electron- first injection transportelectron-transport injection second electrode layer layer light-emittinglayer layer layer electrode light-emitting ITSO DBT3P- PCBBiSF2mDBTBPDBq- 2mDBTBPDBq-II BPhen LiF Al element 6 110 nm II:MoOx 20 nmII:PCBBiSF:[Ir(dppm)₂(acac)] 20 nm 20 nm 1 nm 200 nm light-emitting(=4:2) BPAFLP (=0.7:0.3:0.05) (=0.8:0.2:0.05) element 7 20 nm 20 nm 20nm 20 nm

The light-emitting element 6 and the light-emitting element 7 were eachsealed using a glass substrate in a glove box containing a nitrogenatmosphere so as not to be exposed to the air. Then, operationalcharacteristics of these light-emitting elements were measured. Notethat the measurements were carried out at room temperature (in anatmosphere kept at 25° C.).

FIG. 17 shows luminance-current efficiency characteristics of thelight-emitting elements of this example. In FIG. 17, the horizontal axisrepresents luminance (cd/m²), and the vertical axis represents currentefficiency (cd/A). FIG. 18 shows voltage-luminance characteristics. InFIG. 18, the horizontal axis represents voltage (V), and the verticalaxis represents luminance (cd/m²). FIG. 19 shows luminance-powerefficiency characteristics. In FIG. 19, the horizontal axis representsluminance (cd/m²), and the vertical axis represents power efficiency(lm/W). FIG. 20 shows luminance-external quantum efficiencycharacteristics. In FIG. 20, the horizontal axis represents luminance(cd/m²), and the vertical axis represents external quantum efficiency(%). Table 6 shows the voltage (V), current density (mA/cm²), CIEchromaticity coordinates (x, y), current efficiency (cd/A), powerefficiency (lm/W), and external quantum efficiency (%) of thelight-emitting element 6 and the light-emitting element 7 at a luminanceof around 1000 cd/m².

TABLE 6 current current power external voltage density chromaticityluminance efficiency efficiency quantum (V) (mA/cm²) x y (cd/m²) (cd/A)(lm/W) efficiency (%) light-emitting 2.8 1.1 0.56 0.44 900 85 96 31element 6 comparative 3.0 1.1 0.55 0.44 1000 87 92 31 light-emittingelement 7

As shown in Table 6, the CIE chromaticity coordinates of thelight-emitting element 6 at a luminance of 900 cd/m² were (x, y)=(0.56,0.44), and the CIE chromaticity coordinates of the light-emittingelement 7 at a luminance of 1000 cd/m² were (x, y)=(0.55, 0.44). It hasbeen found that orange light emission originating from [Ir(dppm)₂(acac)]was obtained from the light-emitting element 6 and the light-emittingelement 7.

FIGS. 17 to 20 and Table 6 show that the light-emitting element 6 andthe light-emitting element 7 can each be driven at low voltage and havehigh current efficiency, high power efficiency, and high externalquantum efficiency. Since the tertiary amine used for the light-emittinglayer of each of the light-emitting element 6 and the light-emittingelement 7 of one embodiment of the present invention has a biphenylamineskeleton and a spirofluorenylamine skeleton, it has a highhole-transport property and a high electron-blocking property and alsoan excellent exciton-blocking property. Therefore, electron leakage andexciton diffusion can be prevented even in a high luminance region, andthus a light-emitting element exhibiting high emission efficiency can beobtained. Further, in accordance with one embodiment of the presentinvention, the drive voltage can be decreased with high emissionefficiency maintained (without lowering emission efficiency) by the useof the same compound as the tertiary amine contained in thelight-emitting layer for the hole-transport layer as in thelight-emitting element 6.

Example 4

In this example, a light-emitting element of one embodiment of thepresent invention will be described with reference to FIG. 7. Note thatchemical formulae of materials used in this example are already shown.

Methods for manufacturing a light-emitting element 8 and a comparativelight-emitting element 9 of this example will be described below.

(Light-Emitting Element 8)

First, in a manner similar to that of the light-emitting element 1, afirst electrode 1101, a hole-injection layer 1111, and a hole-transportlayer 1112 were formed over a glass substrate 1100. The thickness of thehole-injection layer 1111 was set to 20 nm.

Further, a light-emitting layer 1113 was formed over the hole-transportlayer 1112 by co-evaporation of 2mDBTBPDBq-II, PCBBiF, and[Ir(dppm)₂(acac)]. Here, a 20 nm thick layer formed with the weightratio of 2mDBTBPDBq-II to PCBBiF and [Ir(dppm)₂(acac)] adjusted to0.7:0.3:0.05 (=2mDBTBPDBq-II:PCBBiF:[Ir(dppm)₂(acac)]) and a 20 nm thicklayer formed with the weight ratio of 2mDBTBPDBq-II to PCBBiF and[Ir(dppm)₂(acac)] adjusted to 0.8:0.2:0.05(=2mDBTBPDBq-II:PCBBiF:[Ir(dppm)₂(acac)]) were stacked.

Then, an electron-transport layer 1114 was formed over thelight-emitting layer 1113 in such a way that a 20 nm thick film of2mDBTBPDBq-II was formed and a 20 nm thick film of BPhen was formed.

After that, over the electron-transport layer 1114, a film of LiF wasformed by evaporation to a thickness of 1 nm to form anelectron-injection layer 1115.

Lastly, aluminum was deposited by evaporation to a thickness of 200 nmto form a second electrode 1103 functioning as a cathode. Thus, thelight-emitting element 8 of this example was fabricated.

Note that in all the above evaporation steps, evaporation was performedby a resistance-heating method.

(Comparative Light-Emitting Element 9)

A light-emitting layer 1113 of the comparative light-emitting element 9was formed by co-evaporation of 2mDBTBPDBq-II and [Ir(dppm)₂(acac)].Here, the weight ratio of 2mDBTBPDBq-II to [Ir(dppm)₂(acac)] wasadjusted to 1:0.05 (=2mDBTBPDBq-II:[Ir(dppm)₂(acac)]). The thickness ofthe light-emitting layer 1113 was set to 40 nm. An electron-transportlayer 1114 of the comparative light-emitting element 9 was formed insuch a way that a 10 nm thick film of 2mDBTBPDBq-II was formed andfurthermore a 15 nm thick film of BPhen was formed. Components otherthan the light-emitting layer 1113 and the electron-transport layer 1114were manufactured in a manner similar to that of the light-emittingelement 8.

Table 7 shows element structures of the light-emitting elements obtainedas described above in this example.

TABLE 7 hole- hole- electron- first injection transportelectron-transport injection second electrode layer layer light-emittinglayer layer layer electrode light-emitting ITSO DBT3P- BPAFLP2mDBTBPDBq- 2mDBTBPDBq-II BPhen LiF Al element 8 110 nm II:MoOx 20 nmII:PCBBiF:[Ir(dppm)₂(acac)] 20 nm 20 nm 1 nm 200 nm (=4:2)(=0.7:0.3:0.05) (=0.8:0.2:0.05) 20 nm 20 nm 20 nm comparative2mDBTBPDBq- 2mDBTBPDBq-II BPhen light-emitting II:[Ir(dppm)₂(acac)] 10nm 15 nm element 9 (=1:0.05) 40 nm

The light-emitting element 8 and the comparative light-emitting element9 were each sealed using a glass substrate in a glove box containing anitrogen atmosphere so as not to be exposed to the air. Then,operational characteristics of these light-emitting elements weremeasured. Note that the measurements were carried out at roomtemperature (in an atmosphere kept at 25° C.).

FIG. 27 shows voltage-current characteristics of the light-emittingelements of this example. In FIG. 27, the horizontal axis representsvoltage (V), and the vertical axis represents current (mA). FIG. 28shows luminance-external quantum efficiency characteristics. In FIG. 28,the horizontal axis represents luminance (cd/m²), and the vertical axisrepresents external quantum efficiency (%). FIG. 29 shows emissionspectra of the light-emitting elements of this example. Table 8 showsthe voltage (V), current density (mA/cm²), CIE chromaticity coordinates(x, y), current efficiency (cd/A), power efficiency (lm/W), and externalquantum efficiency (%) of each of the light-emitting elements at aluminance of around 1000 cd/m².

TABLE 8 current current power external voltage density chromaticityluminance efficiency efficiency quantum (V) (mA/cm²) x y (cd/m²) (cd/A)(lm/W) efficiency (%) light-emitting 2.8 1.1 0.56 0.44 960 85 95 31element 8 comparative 3.3 2.1 0.56 0.44 1100 53 50 21 light-emittingelement 9

As shown in Table 8, the CIE chromaticity coordinates of thelight-emitting element 8 at a luminance of 960 cd/m² were (x, y)=(0.56,0.44). The CIE chromaticity coordinates of the comparativelight-emitting element 9 at a luminance of 1100 cd/m² were (x, y)=(0.56,0.44). It has been found that orange light emission originating from[Ir(dppm)₂(acac)] was obtained from the light-emitting elements of thisexample.

The light-emitting element 8 shows an extremely high external quantumefficiency of 31% (corresponding to a current efficiency of 85 cd/A) ataround 1000 cd/m², which is higher than that of the comparativelight-emitting element 9 that does not involve energy transfer from anexciplex.

In addition, the light-emitting element 8 shows an extremely low voltageof 2.8 V at around 1000 cd/m², and the voltage is lower than that of thecomparative light-emitting element 9.

Next, the light-emitting element 8 and the comparative light-emittingelement 9 were subjected to reliability tests. Results of thereliability tests are shown in FIG. 30. In FIG. 30, the vertical axisrepresents normalized luminance (%) with an initial luminance of 100%,and the horizontal axis represents driving time (h) of the elements. Inthe reliability tests, the light-emitting elements of this example weredriven at room temperature under the conditions where the initialluminance was set to 5000 cd/m² and the current density was constant.FIG. 30 shows that the light-emitting element 8 kept 89% of the initialluminance after 3400 hours elapsed and the luminance of the comparativelight-emitting element 9 was less than 89% of the initial luminanceafter 230 hours elapsed. The results of the reliability tests haverevealed that the light-emitting element 8 has a longer lifetime thanthe comparative light-emitting element 9.

As described above, it has been found that a light-emitting elementexhibiting high emission efficiency can be obtained in accordance withone embodiment of the present invention. It has also been found that alight-emitting element having a long lifetime can be obtained inaccordance with one embodiment of the present invention.

Example 5

In this example, a light-emitting element of one embodiment of thepresent invention will be described with reference to FIG. 7. Chemicalformulae of materials used in this example are shown below. Note thatthe chemical formulae of the materials already shown above are omitted.

Methods for manufacturing a light-emitting element 10, a light-emittingelement 11, and a comparative light-emitting element 12 of this examplewill be described below. Note that components other than alight-emitting layer of each light-emitting element of this example andmanufacturing methods thereof are similar to those of the light-emittingelement 8; thus, the description is omitted here. The light-emittinglayer of each light-emitting element of this example and themanufacturing method thereof will be described below.

(Light-Emitting Element 10)

In the light-emitting element 10, a light-emitting layer 1113 was formedover a hole-transport layer 1112 by co-evaporation of 2mDBTBPDBq-II,N-(4-biphenyl)-N-(9,9-dimethyl-9H-fluoren-2-yl)-9-phenyl-9H-carbazol-3-amine(abbreviation: PCBiF), and [Ir(dppm)₂(acac)]. Here, a 20 nm thick layerformed with the weight ratio of 2mDBTBPDBq-II to PCBiF and[Ir(dppm)₂(acac)] adjusted to 0.7:0.3:0.05(=2mDBTBPDBq-II:PCBiF:[Ir(dppm)₂(acac)]) and a 20 nm thick layer formedwith the weight ratio of 2mDBTBPDBq-II to PCBiF and [Ir(dppm)₂(acac)]adjusted to 0.8:0.2:0.05 (=2mDBTBPDBq-II:PCBiF:[Ir(dppm)₂(acac)]) werestacked.

(Light-Emitting Element 11)

In the light-emitting element 11, a light-emitting layer 1113 was formedover a hole-transport layer 1112 by co-evaporation of 2mDBTBPDBq-II,N-(4-biphenyl)-N-(9,9′-spirobi[9H-fluoren]-2-yl)-9-phenyl-9H-carbazol-3-amine(abbreviation: PCBiSF), and [Ir(dppm)₂(acac)]. Here, a 20 nm thick layerformed with the weight ratio of 2mDBTBPDBq-II to PCBiSF and[Ir(dppm)₂(acac)] adjusted to 0.7:0.3:0.05(=2mDBTBPDBq-II:PCBiSF:[Ir(dppm)₂(acac)]) and a 20 nm thick layer formedwith the weight ratio of 2mDBTBPDBq-II to PCBiSF and [Ir(dppm)₂(acac)]adjusted to 0.8:0.2:0.05 (=2mDBTBPDBq-II:PCBiSF:[Ir(dppm)₂(acac)]) werestacked.

(Comparative Light-Emitting Element 12)

In the comparative light-emitting element 12, a light-emitting layer1113 was formed over a hole-transport layer 1112 by co-evaporation of2mDBTBPDBq-II,2-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-spiro-9,9′-bifluorene(abbreviation: PCASF), and [Ir(dppm)₂(acac)]. Here, a 20 nm thick layerformed with the weight ratio of 2mDBTBPDBq-II to PCASF and[Ir(dppm)₂(acac)] adjusted to 0.7:0.3:0.05(=2mDBTBPDBq-II:PCASF:[Ir(dppm)₂(acac)]) and a 20 nm thick layer formedwith the weight ratio of 2mDBTBPDBq-II to PCASF and [Ir(dppm)₂(acac)]adjusted to 0.8:0.2:0.05 (=2mDBTBPDBq-II:PCASF:[Ir(dppm)₂(acac)]) werestacked.

Table 9 shows element structures of the light-emitting elements obtainedas described above in this example.

TABLE 9 hole- hole- electron- first injection transportelectron-transport injection second electrode layer layer light-emittinglayer layer layer electrode light-emitting ITSO DBT3P- BPAFLP2mDBTBPDBq- 2mDBTBPDBq-II BPhen LiF Al element 10 110 nm II:MoOx 20 nmII:PCBiF:[Ir(dppm)₂(acac)] 20 nm 20 nm 1 nm 200 nm (=4:2)(=0.7:0.3:0.05) (=0.8:0.2:0.05) 20 nm 20 nm 20 nm light-emitting2mDBTBPDBq- element 11 II:PCBiSF:[Ir(dppm)₂(acac)] (=0.7:0.3:0.05)(=0.8:0.2:0.05) 20 nm 20 nm comparative 2mDBTBPDBq- light-emittingII:PCASF:[Ir(dppm)₂(acac)] element 12 (=0.7:0.3:0.05) (=0.8:0.2:0.05) 20nm 20 nm

The light-emitting element 10, the light-emitting element 11, and thecomparative light-emitting element 12 were each sealed using a glasssubstrate in a glove box containing a nitrogen atmosphere so as not tobe exposed to the air. Then, operational characteristics of theselight-emitting elements were measured. Note that the measurements werecarried out at room temperature (in an atmosphere kept at 25° C.).

FIG. 31 shows luminance-current efficiency characteristics of thelight-emitting elements of this example. In FIG. 31, the horizontal axisrepresents luminance (cd/m²), and the vertical axis represents currentefficiency (cd/A). FIG. 32 shows voltage-luminance characteristics. InFIG. 32, the horizontal axis represents voltage (V), and the verticalaxis represents luminance (cd/m²). FIG. 33 shows luminance-externalquantum efficiency characteristics. In FIG. 33, the horizontal axisrepresents luminance (cd/m²), and the vertical axis represents externalquantum efficiency (%). Further, Table 10 shows the voltage (V), currentdensity (mA/cm²), CIE chromaticity coordinates (x, y), currentefficiency (cd/A), power efficiency (lm/W), and external quantumefficiency (%) of each of the light-emitting elements at a luminance ofaround 1000 cd/m².

TABLE 10 current current power external voltage density chromaticityluminance efficiency efficiency quantum (V) (mA/cm²) x y (cd/m²) (cd/A)(lm/W) efficiency (%) light-emitting 3.2 1.4 0.57 0.43 960 70 69 29element 10 light-emitting 3.3 1.5 0.57 0.43 1000 70 67 29 element 11comparative 3.3 1.4 0.57 0.43 930 65 62 27 light-emitting element 12

As shown in Table 10, the CIE chromaticity coordinates of eachlight-emitting element at a luminance of around 1000 cd/m² were (x,y)=(0.57, 0.43). It has been found that orange light emissionoriginating from [Ir(dppm)₂(acac)] was obtained from the light-emittingelements of this example.

FIG. 32 and Table 10 show that the light-emitting element 10, thelight-emitting element 11, and the comparative light-emitting element 12are driven at comparable voltages. FIG. 31, FIG. 33, and Table 10 showthat the light-emitting element 10 and the light-emitting element 11have higher current efficiency, higher power efficiency, and higherexternal quantum efficiency than the comparative light-emitting element12.

Next, the light-emitting element 10, the light-emitting element 11, andthe comparative light-emitting element 12 were subjected to reliabilitytests. Results of the reliability tests are shown in FIG. 34. In FIG.34, the vertical axis represents normalized luminance (%) with aninitial luminance of 100%, and the horizontal axis represents drivingtime (h) of the elements. In the reliability tests, the light-emittingelements of this example were driven at room temperature under theconditions where the initial luminance was set to 5000 cd/m² and thecurrent density was constant. FIG. 34 shows that the light-emittingelement 10 kept 94% of the initial luminance after 660 hours elapsed,the light-emitting element 11 kept 93% of the initial luminance after660 hours elapsed, and the luminance of the comparative light-emittingelement 12 was less than 87% of the initial luminance after 660 hourselapsed. The results of the reliability tests have revealed that thelight-emitting element 10 and the light-emitting element 11 have alonger lifetime than the comparative light-emitting element 12.

In the light-emitting element 11, the light-emitting layer containsPCBiSF which has a spirofluorenyl group, a biphenyl group, and asubstituent including a carbazole skeleton. In the comparativelight-emitting element 12, the light-emitting layer contains PCASF whichhas a spirofluorenyl group, a phenyl group, and a substituent includinga carbazole skeleton. That is, the only difference between thelight-emitting element 11 and the comparative light-emitting element 12is whether the substituent of the tertiary amine contained in thelight-emitting layer is a biphenyl group or a phenyl group. The tertiaryamine used in the light-emitting element 11 of one embodiment of thepresent invention forms a p-biphenylamine skeleton in which the4-position of the phenyl group of the highly reactive phenylamineskeleton is capped with the phenyl group. Thus, a highly reliablelight-emitting element can be obtained.

As described above, it has been found that a light-emitting elementexhibiting high emission efficiency can be obtained in accordance withone embodiment of the present invention. It has also been found that alight-emitting element having a long lifetime can be obtained inaccordance with one embodiment of the present invention.

Example 6

In this example, a light-emitting element of one embodiment of thepresent invention will be described with reference to FIG. 7. Note thatchemical formulae of materials used in this example are already shown.

Methods for manufacturing a light-emitting element 13, a light-emittingelement 14, a light-emitting element 15, and a comparativelight-emitting element 16 of this example will be described below. Notethat components other than a light-emitting layer and anelectron-transport layer of each light-emitting element of this exampleand manufacturing methods thereof are similar to those of thelight-emitting element 8; thus, the description is omitted here. Thelight-emitting layer and the electron-transport layer of eachlight-emitting element of this example and the manufacturing methodthereof will be described below.

(Light-Emitting Element 13)

In the light-emitting element 13, a light-emitting layer 1113 was formedover a hole-transport layer 1112 by co-evaporation of 2mDBTBPDBq-II,PCBBiF, and [Ir(tBuppm)₂(acac)]. Here, a 20 nm thick layer formed withthe weight ratio of 2mDBTBPDBq-II to PCBBiF and [Ir(tBuppm)₂(acac)]adjusted to 0.7:0.3:0.05 (=2mDBTBPDBq-II:PCBBiF:[Ir(tBuppm)₂(acac)]) anda 20 nm thick layer formed with the weight ratio of 2mDBTBPDBq-II toPCBBiF and [Ir(tBuppm)₂(acac)] adjusted to 0.8:0.2:0.05(=2mDBTBPDBq-II:PCBBiF:[Ir(tBuppm)₂(acac)]) were stacked.

(Light-Emitting Element 14)

In the light-emitting element 14, a light-emitting layer 1113 was formedover a hole-transport layer 1112 by co-evaporation of 2mDBTBPDBq-II,PCBiF, and [Ir(tBuppm)₂(acac)]. Here, a 20 nm thick layer formed withthe weight ratio of 2mDBTBPDBq-II to PCBiF and [Ir(tBuppm)₂(acac)]adjusted to 0.7:0.3:0.05 (=2mDBTBPDBq-II:PCBiF:[Ir(tBuppm)₂(acac)]) anda 20 nm thick layer formed with the weight ratio of 2mDBTBPDBq-II toPCBiF and [Ir(tBuppm)₂(acac)] adjusted to 0.8:0.2:0.05(=2mDBTBPDBq-II:PCBiF:[Ir(tBuppm)₂(acac)]) were stacked.

(Light-Emitting Element 15)

In the light-emitting element 15, a light-emitting layer 1113 was formedover a hole-transport layer 1112 by co-evaporation of 2mDBTBPDBq-II,PCBiSF, and [Ir(tBuppm)₂(acac)]. Here, a 20 nm thick layer formed withthe weight ratio of 2mDBTBPDBq-II to PCBiSF and [Ir(tBuppm)₂(acac)]adjusted to 0.7:0.3:0.05 (=2mDBTBPDBq-II:PCBiSF:[Ir(tBuppm)₂(acac)]) anda 20 nm thick layer formed with the weight ratio of 2mDBTBPDBq-II toPCBiSF and [Ir(tBuppm)₂(acac)] adjusted to 0.8:0.2:0.05(=2mDBTBPDBq-II:PCBiSF:[Ir(tBuppm)₂(acac)]) were stacked.

(Comparative Light-Emitting Element 16)

In the comparative light-emitting element 16, a light-emitting layer1113 was formed over a hole-transport layer 1112 by co-evaporation of2mDBTBPDBq-II, PCASF, and [Ir(tBuppm)₂(acac)]. Here, a 20 nm thick layerformed with the weight ratio of 2mDBTBPDBq-II to PCASF and[Ir(tBuppm)₂(acac)] adjusted to 0.7:0.3:0.05(=2mDBTBPDBq-II:PCASF:[Ir(tBuppm)₂(acac)]) and a 20 nm thick layerformed with the weight ratio of 2mDBTBPDBq-II to PCASF and[Ir(tBuppm)₂(acac)] adjusted to 0.8:0.2:0.05(=2mDBTBPDBq-II:PCASF:[Ir(tBuppm)₂(acac)]) were stacked.

Further, in each of the light-emitting element 13, the light-emittingelement 14, the light-emitting element 15, and the comparativelight-emitting element 16, an electron-transport layer 1114 was formedover the light-emitting layer 1113 in such a way that a 10 nm thick filmof 2mDBTBPDBq-II was formed and a 15 nm thick film of BPhen was formed.

Table 11 shows element structures of the light-emitting elementsobtained as described above in this example.

TABLE 11 hole- hole- electron- first injection transportelectron-transport injection second electrode layer layer light-emittinglayer layer layer electrode light-emitting ITSO DBT3P- BPAFLP2mDBTBPDBq- 2mDBTBPDBq-II BPhen LiF Al element 13 110 nm II:MoOx 20 nmII:PCBBiF:[Ir(tBuppm)₂(acac)] 10 nm 15 nm 1 nm 200 nm (=4:2)(=0.7:0.3:0.05) (=0.8:0.2:0.05) 20 nm 20 nm 20 nm light-emitting2mDBTBPDBq- element 14 II:PCBiF:[Ir(tBuppm)₂(acac)] (=0.7:0.3:0.05)(=0.8:0.2:0.05) 20 nm 20 nm light-emitting 2mDBTBPDBq- element 15II:PCBiSF:[Ir(tBuppm)₂(acac)] (=0.7:0.3:0.05) (=0.8:0.2:0.05) 20 nm 20nm comparative 2mDBTBPDBq- light-emitting II:PCASF:[Ir(tBuppm)₂(acac)]element 16 (=0.7:0.3:0.05) (=0.8:0.2:0.05) 20 nm 20 nm

The light-emitting element 13, the light-emitting element 14, thelight-emitting element 15, and the comparative light-emitting element 16were each sealed using a glass substrate in a glove box containing anitrogen atmosphere so as not to be exposed to the air. Then,operational characteristics of these light-emitting elements weremeasured. Note that the measurements were carried out at roomtemperature (in an atmosphere kept at 25° C.).

FIG. 35 shows luminance-current efficiency characteristics of thelight-emitting elements of this example. In FIG. 35, the horizontal axisrepresents luminance (cd/m²), and the vertical axis represents currentefficiency (cd/A). FIG. 36 shows voltage-luminance characteristics. InFIG. 36, the horizontal axis represents voltage (V), and the verticalaxis represents luminance (cd/m²). FIG. 37 shows luminance-externalquantum efficiency characteristics. In FIG. 37, the horizontal axisrepresents luminance (cd/m²), and the vertical axis represents externalquantum efficiency (%). Further, Table 12 shows the voltage (V), currentdensity (mA/cm²), CIE chromaticity coordinates (x, y), currentefficiency (cd/A), power efficiency (lm/W), and external quantumefficiency (%) of each light-emitting element at a luminance of around1000 cd/m².

TABLE 12 current current power external voltage density chromaticityluminance efficiency efficiency quantum (V) (mA/cm²) x y (cd/m²) (cd/A)(lm/W) efficiency (%) light-emitting 2.8 0.80 0.41 0.58 860 107 120 28element 13 light-emitting 2.9 0.89 0.41 0.58 970 109 118 29 element 14light-emitting 2.9 0.95 0.42 0.57 1000 109 119 29 element 15 comparative3.0 0.10 0.42 0.57 1100 109 114 29 light-emitting element 16

As shown in Table 12, the CIE chromaticity coordinates of thelight-emitting element 13 at a luminance of 860 cd/m² were (x, y)=(0.41,0.58). The CIE chromaticity coordinates of the light-emitting element 14at a luminance of 970 cd/m² were (x, y)=(0.41, 0.58). The CIEchromaticity coordinates of the light-emitting element 15 at a luminanceof 1000 cd/m² were (x, y)=(0.42, 0.57). The CIE chromaticity coordinatesof the comparative light-emitting element 16 at a luminance of 1100cd/m² were (x, y)=(0.42, 0.57). It has been found that yellow-greenlight emission originating from [Ir(tBuppm)₂(acac)] was obtained fromthe light-emitting elements of this example.

FIGS. 35 to 37 and Table 12 show that the light-emitting element 13, thelight-emitting element 14, the light-emitting element 15, and thecomparative light-emitting element 16 can each be driven at low voltageand have high current efficiency, high power efficiency, and highexternal quantum efficiency.

Next, the light-emitting element 13, the light-emitting element 14, thelight-emitting element 15, and the comparative light-emitting element 16were subjected to reliability tests. Results of the reliability testsare shown in FIG. 38. In FIG. 38, the vertical axis representsnormalized luminance (%) with an initial luminance of 100%, and thehorizontal axis represents driving time (h) of the elements. In thereliability tests, the light-emitting elements of this example weredriven at room temperature under the conditions where the initialluminance was set to 5000 cd/m² and the current density was constant.FIG. 38 shows that the light-emitting element 13 kept 90% of the initialluminance after 520 hours elapsed, the light-emitting element 14 kept84% of the initial luminance after 600 hours elapsed, the light-emittingelement 15 kept 85% of the initial luminance after 520 hours elapsed,and the luminance of the comparative light-emitting element 16 was lessthan 75% of the initial luminance after 600 hours elapsed. The resultsof the reliability tests have revealed that the light-emitting element13, the light-emitting element 14, and the light-emitting element 15have a longer lifetime than the comparative light-emitting element 16.

As described above, the light-emitting element 15 kept 85% of theinitial luminance after 520 hours elapsed, but the luminance of thecomparative light-emitting element 16 is less than 77% of the initialluminance after 520 hours elapsed. In the light-emitting element 15, thelight-emitting layer contains PCBiSF which has a spirofluorenyl group, abiphenyl group, and a substituent including a carbazole skeleton. In thecomparative light-emitting element 16, the light-emitting layer containsPCASF which has a spirofluorenyl group, a phenyl group, and asubstituent including a carbazole skeleton. That is, the only differencebetween the light-emitting element 15 and the comparative light-emittingelement 16 is whether the substituent of the tertiary amine contained inthe light-emitting layer is a biphenyl group or a phenyl group. Thetertiary amine used in the light-emitting element 15 of one embodimentof the present invention forms a p-biphenylamine skeleton in which the4-position of the phenyl group of the highly reactive phenylamineskeleton is capped with the phenyl group. Thus, a highly reliablelight-emitting element can be obtained.

As described above, it has been found that a light-emitting elementexhibiting high emission efficiency can be obtained in accordance withone embodiment of the present invention. It has also been found that alight-emitting element having a long lifetime can be obtained inaccordance with one embodiment of the present invention.

Example 7

In this example, a light-emitting element of one embodiment of thepresent invention will be described with reference to FIG. 7. Chemicalformulae of materials used in this example are shown below. Note thatthe chemical formulae of the materials already shown above are omitted.

A method for manufacturing a light-emitting element 17 of this examplewill be described below.

(Light-Emitting Element 17)

First, in a manner similar to that of the light-emitting element 8, afirst electrode 1101, a hole-injection layer 1111, and a hole-transportlayer 1112 were formed over a glass substrate 1100.

Next, a light-emitting layer 1113 was formed over the hole-transportlayer 1112 by co-evaporation of4,6-bis[3-(9H-carbazol-9-yl)phenyl]pyrimidine (abbreviation:4,6mCzP2Pm), PCBBiF, and [Ir(tBuppm)₂(acac)]. Here, a 20 nm thick layerformed with the weight ratio of 4,6mCzP2Pm to PCBBiF and[Ir(tBuppm)₂(acac)] adjusted to 0.7:0.3:0.05(=4,6mCzP2Pm:PCBBiF:[Ir(tBuppm)₂(acac)]) and a 20 nm thick layer formedwith the weight ratio of 4,6mCzP2Pm to PCBBiF and [Ir(tBuppm)₂(acac)]adjusted to 0.8:0.2:0.05 (=4,6mCzP2Pm:PCBBiF:[Ir(tBuppm)₂(acac)]) werestacked.

Then, an electron-transport layer 1114 was formed over thelight-emitting layer 1113 in such a way that a 15 nm thick film of4,6mCzP2Pm was formed and a 10 nm thick film of BPhen was formed.

After that, over the electron-transport layer 1114, a film of LiF wasformed by evaporation to a thickness of 1 nm to form anelectron-injection layer 1115.

Lastly, aluminum was deposited by evaporation to a thickness of 200 nmto form a second electrode 1103 functioning as a cathode. Thus, thelight-emitting element 17 of this example was fabricated.

Note that in all the above evaporation steps, evaporation was performedby a resistance-heating method.

Table 13 shows an element structure of the light-emitting elementobtained as described above in this example.

TABLE 13 hole- hole- electron- first injection transportelectron-transport injection second electrode layer layer light-emittinglayer layer layer electrode light-emitting ITSO DBT3P- BPAFLP4.6mCzP2Pm:PCBBiF:[Ir(tBuppm)₂(acac)] 4.6mCzP2Pm BPhen LiF Al element 17110 nm II:MoOx 20 nm (=0.7:0.3:0.05) (=0.8:0.2:0.05) 15 nm 10 nm 1 nm200 nm (=4:2) 20 nm 20 nm 20 nm

The light-emitting element 17 was sealed using a glass substrate in aglove box containing a nitrogen atmosphere so as not to be exposed tothe air. Then, operational characteristics of the light-emitting elementwere measured. Note that the measurements were carried out at roomtemperature (in an atmosphere kept at 25° C.).

FIG. 39 shows luminance-current efficiency characteristics of thelight-emitting element of this example. In FIG. 39, the horizontal axisrepresents luminance (cd/m²), and the vertical axis represents currentefficiency (cd/A). FIG. 40 shows voltage-luminance characteristics. InFIG. 40, the horizontal axis represents voltage (V), and the verticalaxis represents luminance (cd/m²). FIG. 41 shows luminance-externalquantum efficiency characteristics. In FIG. 41, the horizontal axisrepresents luminance (cd/m²), and the vertical axis represents externalquantum efficiency (%). Table 14 shows the voltage (V), current density(mA/cm²), CIE chromaticity coordinates (x, y), current efficiency(cd/A), power efficiency (lm/W), and external quantum efficiency (%) ofthe light-emitting element 17 at a luminance of 760 cd/m².

TABLE 14 current current power external voltage density chromaticityefficiency efficiency quantum (V) (mA/cm²) x y (cd/A) (lm/W) efficiency(%) light-emitting 2.8 0.67 0.41 0.58 113 127 30 element 17

As shown in Table 14, the CIE chromaticity coordinates of thelight-emitting element 17 at a luminance of 760 cd/m² were (x, y)=(0.41,0.58). It has been found that orange light emission originating from[Ir(tBuppm)₂(acac)] was obtained from the light-emitting element of thisexample.

FIGS. 39 to 41 and Table 14 show that the light-emitting element 17 canbe driven at low voltage and has high current efficiency, high powerefficiency, and high external quantum efficiency.

Next, the light-emitting element 17 was subjected to a reliability test.Results of the reliability test are shown in FIG. 42. In FIG. 42, thevertical axis represents normalized luminance (%) with an initialluminance of 100%, and the horizontal axis represents driving time (h)of the element. In the reliability test, the light-emitting element ofthis example was driven at room temperature under the conditions wherethe initial luminance was set to 5000 cd/m² and the current density wasconstant. FIG. 42 shows that the light-emitting element 17 kept 90% ofthe initial luminance after 180 hours elapsed.

As described above, it has been found that a light-emitting elementexhibiting high emission efficiency can be obtained in accordance withone embodiment of the present invention. It has also been found that alight-emitting element having a long lifetime can be obtained inaccordance with one embodiment of the present invention.

Reference Example 1

A method for synthesizingN-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine(abbreviation: PCBBiF) used in Examples 1, 2, and 4 and represented bythe following structural formula (128) will be described.

Step 1: Synthesis ofN-(1,1′-biphenyl-4-yl-9,9-dimethyl-N-phenyl-9H-fluoren-2-amine

A synthesis scheme of Step 1 is shown in (x-1).

In a 1 L three-neck flask were placed 45 g (0.13 mol) ofN-(1,1′-biphenyl-4-yl)-9,9-dimethyl-9H-fluoren-2-amine, 36 g (0.38 mol)of sodium tert-butoxide, 21 g (0.13 mol) of bromobenzene, and 500 mL oftoluene. The mixture was degassed by being stirred while the pressurewas being reduced, and after the degassing, the atmosphere in the flaskwas replaced with nitrogen. Then, 0.8 g (1.4 mmol) ofbis(dibenzylideneacetone)palladium(0) and 12 mL (5.9 mmol) oftri(tert-butyl)phosphine (a 10 wt % hexane solution) were added.

The mixture was stirred under a nitrogen stream at 90° C. for 2 hours.Then, the mixture was cooled to room temperature, and a solid wasseparated by suction filtration. The obtained filtrate was concentratedto give about 200 mL of a brown liquid. The brown liquid was mixed withtoluene, and the resulting solution was purified using Celite(manufactured by Wako Pure Chemical Industries, Ltd., Catalog No.531-16855 (the same applies to Celite in the following description andthe description is repeated)), alumina, Florisil (manufactured by WakoPure Chemical Industries, Ltd., Catalog No. 540-00135 (the same appliesto Florisil in the following description and the description isrepeated)). The resulting filtrate was concentrated to give a lightyellow liquid. The light yellow liquid was recrystallized from hexane togive 52 g of target light yellow powder in a yield of 95%.

Step 2: Synthesis ofN-(1,1′-biphenyl-4-yl)-N-(4-bromophenyl)-9,9-dimethyl-9H-fluoren-2-amine

A synthesis scheme of Step 2 is shown in (x-2).

In a 1 L Mayer flask was placed 45 g (0.10 mol) ofN-(1,1′-biphenyl-4-yl)-9,9-dimethyl-N-phenyl-9H-fluoren-2-amine, whichwas dissolved in 225 mL of toluene by stirring while being heated. Afterthe solution was naturally cooled to room temperature, 225 mL of ethylacetate and 18 g (0.10 mol) of N-bromosuccinimide (abbreviation: NBS)were added, and the mixture was stirred at room temperature for 2.5hours. After the stirring, the mixture was washed three times with asaturated aqueous solution of sodium hydrogen carbonate and once with asaturated aqueous solution of sodium chloride. Magnesium sulfate wasadded to the resulting organic layer, and the mixture was left still for2 hours for drying. The mixture was subjected to gravity filtration toremove magnesium sulfate, and the resulting filtrate was concentrated togive a yellow liquid. The yellow liquid was mixed with toluene, and thesolution was purified using Celite, alumina, and Florisil. The resultingsolution was concentrated to give a light yellow solid. The light yellowsolid was recrystallized from toluene/ethanol to give 47 g of targetwhite powder in a yield of 89%.

Step 3: Synthesis of PCBBiF

A synthesis scheme of Step 3 is shown in (x-3).

In a 1 L three-neck flask were placed 41 g (80 mmol) ofN-(1,1′-biphenyl-4-yl)-N-(4-bromophenyl)-9,9-dimethyl-9H-fluoren-2-amineand 25 g (88 mmol) of 9-phenyl-9H-carbazole-3-boronic acid, to which 240mL of toluene, 80 mL of ethanol, and 120 mL of an aqueous solution ofpotassium carbonate (2.0 mol/L) were added. The mixture was degassed bybeing stirred while the pressure was being reduced, and after thedegassing, the atmosphere in the flask was replaced with nitrogen.Further, 27 mg (0.12 mmol) of palladium(II) acetate and 154 mg (0.5mmol) of tri(ortho-tolyl)phosphine were added. The mixture was degassedagain by being stirred while the pressure was being reduced, and afterthe degassing, the atmosphere in the flask was replaced with nitrogen.The mixture was stirred under a nitrogen stream at 110° C. for 1.5hours.

After the mixture was naturally cooled to room temperature while beingstirred, the aqueous layer of the mixture was extracted twice withtoluene. The resulting solution of the extract and the organic layerwere combined and washed twice with water and twice with a saturatedaqueous solution of sodium chloride. Magnesium sulfate was added to thesolution, and the mixture was left still for drying. The mixture wassubjected to gravity filtration to remove magnesium sulfate, and theresulting filtrate was concentrated to give a brown solution. The brownsolution was mixed with toluene, and the resulting solution was purifiedusing Celite, alumina, and Florisil. The resulting filtrate wasconcentrated to give a light yellow solid. The light yellow solid wasrecrystallized from ethyl acetate/ethanol to give 46 g of target lightyellow powder in a yield of 88%.

By a train sublimation method, 38 g of the obtained light yellow powderwas purified by sublimation. In the sublimation purification, the lightyellow powder was heated at 345° C. under a pressure of 3.7 Pa with anargon flow rate of 15 mL/min. After the sublimation purification, 31 gof a target light yellow solid was obtained at a collection rate of 83%.

This compound was identified asN-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine(abbreviation: PCBBiF), which was the target of the synthesis, bynuclear magnetic resonance (NMR) spectroscopy.

¹H NMR data of the obtained light yellow solid are shown below.

¹H NMR (CDCl₃, 500 MHz): δ=1.45 (s, 6H), 7.18 (d, J=8.0 Hz, 1H),7.27-7.32 (m, 8H), 7.40-7.50 (m, 7H), 7.52-7.53 (m, 2H), 7.59-7.68 (m,12H), 8.19 (d, J=8.0 Hz, 1H), 8.36 (d, J=1.1 Hz, 1H).

FIGS. 21A and 21B show ¹H NMR charts. Note that FIG. 21B is a chartwhere the range of from 6.00 ppm to 10.0 ppm in FIG. 21A is enlarged.

Further, FIG. 22A shows the absorption spectrum of PCBBiF in a toluenesolution of PCBBiF, and FIG. 22B shows the emission spectrum thereof. Inaddition, FIG. 23A shows the absorption spectrum of a thin film ofPCBBiF, and FIG. 23B shows the emission spectrum thereof. Anultraviolet-visible spectrophotometer (V-550, manufactured by JASCOCorporation) was used for the measurements. Samples were prepared insuch a way that the solution was put in a quartz cell and the thin filmwas formed on a quartz substrate by evaporation. Here are shown theabsorption spectrum for the solution which was obtained by subtractingthe absorption spectra of quartz and toluene from those of quartz andthe solution, and the absorption spectrum for the thin film which wasobtained by subtracting the absorption spectrum of the quartz substratefrom those of the quartz substrate and the thin film. In FIGS. 22A and22B and FIGS. 23A and 23B, the horizontal axis represents wavelength(nm) and the vertical axis represents intensity (arbitrary unit). In thecase of the toluene solution, an absorption peak was found at around 350nm, and peaks of the emission wavelengths were at 401 nm and 420 nm (atan excitation wavelength of 360 nm). In the case of the thin film, anabsorption peak was found at around 356 nm, and peaks of the emissionwavelengths were at 415 nm and 436 nm (at an excitation wavelength of370 nm).

Reference Example 2

A method for synthesizing9,9-dimethyl-N-[4-(1-naphthyl)phenyl]-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9H-fluoren-2-amine(abbreviation: PCBNBF) used in Example 1 will be described.

Step 1: Synthesis of 1-(4-bromophenyl)-naphthalene

A synthesis scheme of Step 1 is shown in (y-1).

To a 3 L three-neck flask were added 47 g (0.28 mol) of1-naphthaleneboronic acid and 82 g (0.29 mol) of 4-bromoiodobenzene andadded 750 mL of toluene and 250 mL of ethanol. The mixture was degassedby being stirred while the pressure was being reduced, and after thedegassing, the atmosphere in the flask was replaced with nitrogen. Tothe solution was added 415 mL of an aqueous solution of potassiumcarbonate (2.0 mol/L). The mixture was degassed again by being stirredwhile the pressure was being reduced, and after the degassing, theatmosphere in the flask was replaced with nitrogen. Further, 4.2 g (14mmol) of tri(ortho-tolyl)phosphine and 0.7 g (2.8 mmol) of palladium(II)acetate were added. This mixture was stirred at 90° C. for 1 hour undera nitrogen stream.

After the stirring, the mixture was naturally cooled to roomtemperature, and the aqueous layer of the mixture was extracted threetimes with toluene. The resulting solution of the extract and theorganic layer were combined and washed twice with water and twice with asaturated aqueous solution of sodium chloride. Then, magnesium sulfatewas added, and the mixture was left still for 18 hours for drying. Themixture was subjected to gravity filtration to remove magnesium sulfate,and the resulting filtrate was concentrated to give an orange liquid.

To the orange liquid was added 500 mL of hexane, and the resultingsolution was purified through Celite and Florisil. The obtained filtratewas concentrated to give a colorless liquid. To the colorless liquid wasadded hexane, and the mixture was left still at −10° C., and theprecipitated impurities were separated by filtration. The resultingfiltrate was concentrated to give a colorless liquid. The colorlessliquid was purified by distillation under reduced pressure, and theresulting yellow liquid was purified by silica gel column chromatography(developing solvent: hexane) to give 56 g of a target colorless liquidin a yield of 72%.

Step 2: Synthesis of9,9-dimethyl-N-(4-naphthyl)phenyl-N-phenyl-9H-fluoren-2-amine

A synthesis scheme of Step 2 is shown in (y-2).

In a 1 L three-neck flask were placed 40 g (0.14 mol) of9,9-dimethyl-N-phenyl-9H-fluoren-2-amine, 40 g (0.42 mol) of sodiumtert-butoxide, and 2.8 g (1.4 mmol) ofbis(dibenzylideneacetone)palladium(0), and added 560 mL of a toluenesolution of 44 g (0.15 mol) of 1-(4-bromophenyl)naphthalene. The mixturewas degassed by being stirred while the pressure was being reduced, andafter the degassing, the atmosphere in the flask was replaced withnitrogen. Then, 14 mL (7.0 mmol) of tri(tert-butyl)phosphine (a 10 wt %hexane solution) was added, and the mixture was stirred under a nitrogenstream at 110° C. for 2 hours.

Then, the mixture was cooled to room temperature, and a solid wasseparated by suction filtration. The obtained filtrate was concentratedto give a dark brown liquid. The dark brown liquid was mixed withtoluene, and the resulting solution was purified through Celite,alumina, and Florisil. The resulting filtrate was concentrated to give alight yellow liquid. The light yellow liquid was recrystallized fromacetonitrile to give 53 g of target light yellow powder in a yield of78%.

Step 3: Synthesis ofN-(4-bromophenyl)-9,9-dimethyl-N-[4-(1-naphthyl)phenyl]-9H-fluoren-2-amine

A synthesis scheme of Step 3 is shown in (y-3).

To a 2 L Mayer flask were added 59 g (0.12 mol) of9,9-dimethyl-N-(4-naphthyl)phenyl-N-phenyl-9H-fluoren-2-amine and 300 mLof toluene, and the mixture was stirred while being heated. After theresulting solution was naturally cooled to room temperature, 300 mL ofethyl acetate and then 21 g (0.12 mol) of N-bromosuccinimide(abbreviation: NBS) were added, and the mixture was stirred at roomtemperature for about 2.5 hours. To the mixture was added 400 mL of asaturated aqueous solution of sodium hydrogen carbonate, and the mixturewas stirred at room temperature. The organic layer of the mixture waswashed twice with a saturated aqueous solution of sodium hydrogencarbonate and twice with a saturated aqueous solution of sodiumchloride. Then, magnesium sulfate was added, and the mixture was leftstill for 2 hours for drying. After the mixture was subjected to gravityfiltration to remove magnesium sulfate, the resulting filtrate wasconcentrated to give a yellow liquid. After the liquid was dissolved intoluene, the solution was purified through Celite, alumina, and Florisilto give a light yellow solid. The obtained light yellow solid wasreprecipitated with toluene/acetonitrile to give 56 g of target whitepowder in a yield of 85%.

Step 4: Synthesis of PCBNBF

A synthesis scheme of Step 4 is shown in (y-4).

In a 1 L three-neck flask were placed 51 g (90 mmol) ofN-(4-bromophenyl)-9,9-dimethyl-N-[4-(1-naphthyl)phenyl]-9H-fluoren-2-amine,28 g (95 mmol) of 9-phenyl-9H-carbazole-3-boronic acid, 0.4 mg (1.8mmol) of palladium(II) acetate, 1.4 g (4.5 mmol) oftri(ortho-tolyl)phosphine, 300 mL of toluene, 100 mL of ethanol, 135 mLof an aqueous solution of sodium carbonate (2.0 mol/L). The mixture wasdegassed by being stirred while the pressure was being reduced, andafter the degassing, the atmosphere in the flask was replaced withnitrogen. The mixture was stirred under a nitrogen stream at 90° C. for1.5 hours. After the stirring, the mixture was cooled to roomtemperature, and a solid was collected by suction filtration. Theorganic layer was extracted from the obtained mixture of the water layerand the organic layer and concentrated to give a brown solid. The brownsolid was recrystallized from toluene/ethyl acetate/ethanol to givetarget white powder. The solid collected after the stirring and thewhite powder obtained by the recrystallization were dissolved intoluene, and the solution was purified through Celite, alumina, andFlorisil. The resulting solution was concentrated and recrystallizedfrom toluene/ethanol to give 54 g of target white powder in a yield of82%.

By a train sublimation method, 51 g of the obtained white powder waspurified by sublimation. In the sublimation purification, the whitepowder was heated at 360° C. under a pressure of 3.7 Pa with an argonflow rate of 15 mL/min. After the sublimation purification, 19 g of atarget light yellow solid was obtained at a collection rate of 38%.

This compound was identified as9,9-dimethyl-N-[4-(1-naphthyl)phenyl]-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9H-fluoren-2-amine(abbreviation: PCBNBF), which was the target of the synthesis, bynuclear magnetic resonance (NMR) spectroscopy.

¹H NMR data of the obtained substance are shown below.

¹H NMR (CDCl₃, 500 MHz): δ=1.50 (s, 6H), 7.21 (dd, J=8.0 Hz, 1.6 Hz,1H), 7.26-7.38 (m, 8H), 7.41-7.44 (m, 5H), 7.46-7.55 (m, 6H), 7.59-7.69(m, 9H), 7.85 (d, J=8.0 Hz, 1H), 7.91 (dd, J=7.5 Hz, 1.7 Hz, 1H),8.07-8.09 (m, 1H), 8.19 (d, J=8.0 Hz, 1H), 8.37 (d, J=1.7 Hz, 1H).

Reference Example 3

A method for synthesizingN-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9′-spirobi[9H-fluoren]-2-amine(abbreviation: PCBBiSF) used in Example 3 and represented by thefollowing structural formula (119) will be described.

Step 1: Synthesis ofN-(1,1′-biphenyl-4-yl)-N-phenyl-9,9′-spirobi[9H-fluoren]-2-amine

A synthesis scheme of Step 1 is shown in (z-1).

In a 200 mL three-neck flask were placed 4.8 g (12 mmol) of2-bromo-9,9-spirobi[9H-fluorene], 3.0 g (12 mmol) of4-phenyl-diphenylamine, 3.5 g (37 mmol) of sodium tert-butoxide, and theatmosphere in the flask was replaced with nitrogen. To the mixture wereadded 60 mL of dehydrated toluene and 0.2 mL of tri(tert-butyl)phoshine(a 10% hexane solution), and the mixture was degassed by being stirredwhile the pressure was being reduced. To the mixture was added 70 mg(0.12 mmol) of bis(dibenzylideneacetone)palladium(0), and the mixturewas heated and stirred under a nitrogen stream at 110° C. for 8 hours.After the stirring, water was added to the mixture, and the aqueouslayer was extracted with toluene. The solution of the extract and theorganic layer were combined and washed with a saturated aqueous solutionof sodium chloride. The organic layer was dried with magnesium sulfate.This mixture was separated by gravity filtration, and the filtrate wasconcentrated to give a solid.

This solid was purified by silica gel column chromatography. In thecolumn chromatography, toluene:hexane=1:5 and then toluene:hexane=1:3were used as developing solvents. The resulting fraction wasconcentrated to give a solid. The obtained solid was recrystallized fromtoluene/ethyl acetate to give 5.7 g of a white solid in a yield of 83%.

Step 2: Synthesis ofN-(1,1′-biphenyl-4-yl)-N-(4-bromophenyl)-9,9′-spirobi[9H-fluoren]-2-amine

A synthesis scheme of Step 2 is shown in (z-2).

To a 100 mL three-neck flask were added 3.0 g (5.4 mmol) ofN-(1,1′-biphenyl-4-yl)-N-phenyl-9,9′-spirobi[9H-fluoren]-2-amine, 20 mLof toluene, and 40 mL of ethyl acetate. To the solution was added 0.93 g(5.2 mmol) of N-bromosuccinimide (abbreviation: NBS), and the mixturewas stirred for 25 hours. After the stirring, the mixture was washedwith water and a saturated aqueous solution of sodium hydrogencarbonate, and then the organic layer was dried over magnesium sulfate.This mixture was separated by gravity filtration, and the filtrate wasconcentrated to give a solid. This solid was purified by silica gelcolumn chromatography. In the column chromatography, hexane and thentoluene:hexane=1:5 were used as developing solvents. The resultingfraction was concentrated to give a solid. The obtained solid wasrecrystallized from ethyl acetate/hexane to give 2.8 g of a white solidin a yield of 83%.

Step 3: Synthesis of PCBBiSF

A synthesis scheme of Step 3 is shown in (z-3).

In a 200 mL three-neck flask were placed 2.4 g (3.8 mmol) ofN-(1,1′-biphenyl-4-yl)-N-(4-bromophenyl)-9,9′-spirobi[9H-fluoren]-2-amine,1.3 g (4.5 mmol) of 9-phenylcarbazole-3-boronic acid, 57 mg (0.19 mmol)of tri(ortho-tolyl)phosphine, and 1.2 g (9.0 mmol) of potassiumcarbonate. To the mixture were added 5 mL of water, 14 mL of toluene,and 7 mL of ethanol, and the mixture was degassed by being stirred underreduced pressure. To this mixture was added 8 mg (0.038 mmol) ofpalladium acetate, and the mixture was stirred under a nitrogen streamat 90° C. for 7.5 hours. After the stirring, the resulting mixture wasextracted with toluene. The obtained solution of the extract and theorganic layer were combined and washed with a saturated aqueous solutionof sodium chloride and then dried over magnesium sulfate. This mixturewas separated by gravity filtration, and the filtrate was concentratedto give a solid. This solid was purified by silica gel columnchromatography. In the column chromatography, toluene:hexane=1:2 andthen toluene:hexane=2:3 were used as developing solvents. The resultingfraction was concentrated to give a solid. The obtained solid wasrecrystallized from ethyl acetate/hexane to give 2.8 g of a target whitesolid in a yield of 94%.

By a train sublimation method, 2.8 g of the obtained solid was purifiedby sublimation. The sublimation purification was performed by heating at336° C. under a pressure of 2.9 Pa with an argon flow rate of 5 mL/min.After the sublimation purification, 0.99 g of a light yellow solid wasobtained at a collection rate of 35%.

This compound was identified asN-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9′-spirobi[9H-fluoren]-2-amine(abbreviation: PCBBiSF), which was the target of the synthesis, bynuclear magnetic resonance (NMR) spectroscopy.

¹H NMR data of the obtained light yellow solid are shown below.

¹H NMR (CDCl₃, 500 MHz): δ=6.67-6.69 (m, 2H), 6.84 (d, J1=7.5 Hz, 2H),7.04-7.11 (m, 5H), 7.13-7.17 (m, 3H), 7.28-7.45 (m, 12H), 7.46-7.53 (m,5H), 7.57-7.64 (m, 5H), 7.74-7.77 (m, 4H), 8.17 (d, J1=7.5 Hz, 1H), 8.27(d, J1=1.5 Hz, 1H).

FIGS. 24A and 24B show ¹H NMR charts. Note that FIG. 24B is a chartwhere the range of from 6.50 ppm to 8.50 ppm in FIG. 24A is enlarged.

Further, FIG. 25A shows the absorption spectrum of PCBBiSF in a toluenesolution of PCBBiSF, and FIG. 25B shows the emission spectrum thereof.In addition, FIG. 26A shows the absorption spectrum of a thin film ofPCBBiSF, and FIG. 26B shows the emission spectrum thereof. Theabsorption spectra were obtained in the same manner as ReferenceExample 1. In FIGS. 25A and 25B and FIGS. 26A and 26B, the horizontalaxis represents wavelength (nm) and the vertical axis representsintensity (arbitrary unit). In the case of the toluene solution, anabsorption peak was found at around 352 nm, and a peak of the emissionwavelength was at 403 nm (at an excitation wavelength of 351 nm). In thecase of the thin film, an absorption peak was found at around 357 nm,and a peak of the emission wavelength was at 424 nm (at an excitationwavelength of 378 nm).

EXPLANATION OF REFERENCE

201: first electrode, 203: EL layer, 203 a: first EL layer, 203 b:second EL layer, 205: second electrode, 207: intermediate layer, 213:light-emitting layer, 221: first organic compound, 222: second organiccompound, 223: phosphorescent compound, 301: hole-injection layer, 302:hole-transport layer, 303: light-emitting layer, 304: electron-transportlayer, 305: electron-injection layer, 306: electron-injection bufferlayer, 307: electron-relay layer, 308: charge-generation region, 401:support substrate, 403: light-emitting element, 405: sealing substrate,407: sealing material, 409 a: first terminal, 409 b: second terminal,411 a: light extraction structure, 411 b: light extraction structure,413: planarization layer, 415: space, 417: auxiliary wiring, 419:insulating layer, 421: first electrode, 423: EL layer, 425: secondelectrode, 501: support substrate, 503: light-emitting element, 505:sealing substrate, 507:

sealing material, 509: FPC, 511: insulating layer, 513: insulatinglayer, 515: space, 517: wiring, 519: partition, 521: first electrode,523: EL layer, 525: second electrode, 531: black matrix, 533: colorfilter, 535: overcoat layer, 541 a: transistor, 541 b: transistor, 542:transistor, 543: transistor, 551: light-emitting portion, 552: drivercircuit portion, 553: driver circuit portion, 1100: glass substrate,1101: first electrode, 1103: second electrode, 1111: hole-injectionlayer, 1112: hole-transport layer, 1113: light-emitting layer, 1114:electron-transport layer, 1115: electron-injection layer, 7100:television device, 7101: housing, 7102: display portion, 7103: stand,7111: remote controller, 7200: computer, 7201: main body, 7202: housing,7203: display portion, 7204: keyboard, 7205: external connection port,7206: pointing device, 7300: portable game machine, 7301 a: housing,7301 b: housing, 7302: joint portion, 7303 a: display portion, 7303 b:display portion, 7304: speaker portion, 7305: recording medium insertionportion, 7306: operation key, 7307: connection terminal, 7308: sensor,7400: cellular phone, 7401: housing, 7402: display portion, 7403:operation button, 7404: external connection port, 7405: speaker, 7406:microphone, 7500: tablet terminal, 7501 a: housing, 7501 b: housing,7502 a: display portion, 7502 b: display portion, 7503: hinge, 7504:power switch, 7505: operation key, 7506: speaker, 7601: lightingportion, 7602: shade, 7603: adjustable arm, 7604: support, 7605: base,7606: power switch, 7701: lamp, 7702: lamp, and 7703: desk lamp.

This application is based on Japanese Patent Application serial no.2012-172944 filed with Japan Patent Office on Aug. 3, 2012 and JapanesePatent Application serial no. 2013-045127 filed with Japan Patent Officeon Mar. 7, 2013, the entire contents of which are hereby incorporated byreference.

The invention claimed is:
 1. A light-emitting device comprising: ananode; a cathode; a light-emitting layer comprising two kinds of organiccompounds which are configured to form an exciplex; and a compound,wherein the light-emitting layer is between the anode and the cathode,wherein the compound is between the anode and the light-emitting layerand represented by General Formula (G0):

wherein each of Ar¹ and Ar² independently represents a substituted orunsubstituted fluorenyl group, a substituted or unsubstitutedspirofluorenyl group, or a substituted or unsubstituted biphenyl group,and wherein Ar³ represents a substituent including a carbazole skeleton.2. The light-emitting device according to claim 1, wherein a layercomprising the compound represented by General Formula (G0) is incontact with the light-emitting layer.
 3. The light-emitting deviceaccording to claim 1, wherein a molecular weight of the compoundrepresented by General Formula (G0) is greater than or equal to 500 andless than or equal to
 2000. 4. A light-emitting device comprising: ananode; a cathode; a light-emitting layer comprising two kinds of organiccompounds which are configured to form an exciplex; a region comprisingan acceptor substance; and a compound, wherein the light-emitting layeris between the anode and the cathode, wherein the region comprising theacceptor substance is between the anode and the light-emitting layer,wherein the compound is between the light-emitting layer and the regioncomprising the acceptor substance and represented by General Formula(G0):

wherein each of Ar¹ and Ar² independently represents a substituted orunsubstituted fluorenyl group, a substituted or unsubstitutedspirofluorenyl group, or a substituted or unsubstituted biphenyl group,and wherein Ar³ represents a substituent including a carbazole skeleton.5. The light-emitting device according to claim 4, wherein the regioncomprising the acceptor substance is a region comprising a substancehaving a high hole-transport property and the acceptor substance.
 6. Thelight-emitting device according to claim 5, wherein a mass ratio of theacceptor substance to the substance having a high hole-transportproperty in the region comprising the acceptor substance is 0.1:1 to4.0:1.
 7. The light-emitting device according to claim 5, wherein thesubstance having a high hole-transport property is an organic compoundhaving a hole mobility of 10⁻⁶ cm²/Vs or more.
 8. The light-emittingdevice according to claim 4, wherein in the region comprising theacceptor substance, a layer comprising a substance having a highhole-transport property and a layer comprising the acceptor substanceare stacked.
 9. The light-emitting device according to claim 8, whereina mass ratio of the acceptor substance to the substance having a highhole-transport property in the region comprising the acceptor substanceis 0.1:1 to 4.0:1.
 10. The light-emitting device according to claim 8,wherein the substance having a high hole-transport property is anorganic compound having a hole mobility of 10⁻⁶ cm²/Vs or more.
 11. Thelight-emitting device according to claim 4, wherein the regioncomprising the acceptor substance is in contact with the anode.
 12. Thelight-emitting device according to claim 4, wherein a molecular weightof the compound represented by General Formula (G0) is greater than orequal to 500 and less than or equal to
 2000. 13. A light-emitting devicecomprising: an anode; a cathode; a light-emitting layer comprising threekinds of compounds; a region comprising an acceptor substance; and acompound, wherein the light-emitting layer is between the anode and thecathode, wherein the region comprising the acceptor substance ispositioned between the anode and the light-emitting layer, wherein thecompound is between the light-emitting layer and the region comprisingthe acceptor substance and represented by General Formula (G0):

wherein each of Ar¹ and Ar² independently represents a substituted orunsubstituted fluorenyl group, a substituted or unsubstitutedspirofluorenyl group, or a substituted or unsubstituted biphenyl group,and wherein Ar³ represents a substituent including a carbazole skeleton.14. The light-emitting device according to claim 13, wherein the regioncomprising the acceptor substance is a region comprising a substancehaving a high hole-transport property and the acceptor substance. 15.The light-emitting device according to claim 14, wherein a mass ratio ofthe acceptor substance to the substance having a high hole-transportproperty in the region comprising the acceptor substance is 0.1:1 to4.0:1.
 16. The light-emitting device according to claim 14, wherein thesubstance having a high hole-transport property is an organic compoundhaving a hole mobility of 10⁻⁶ cm²/Vs or more.
 17. The light-emittingdevice according to claim 13, wherein in the region comprising theacceptor substance, a layer comprising a substance having a highhole-transport property and a layer comprising the acceptor substanceare stacked.
 18. The light-emitting device according to claim 17,wherein a mass ratio of the acceptor substance to the substance having ahigh hole-transport property in the region comprising the acceptorsubstance is 0.1:1 to 4.0:1.
 19. The light-emitting device according toclaim 17, wherein the substance having a high hole-transport property isan organic compound having a hole mobility of 10⁻⁶ cm²/Vs or more. 20.The light-emitting device according to claim 13, wherein the regioncomprising the acceptor substance is in contact with the anode.
 21. Thelight-emitting device according to claim 13, wherein a molecular weightof the compound represented by General Formula (G0) is greater than orequal to 500 and less than or equal to
 2000. 22. A light-emitting devicecomprising: an anode; a cathode; a light-emitting layer comprising twokinds of organic compounds which are configured to form an exciplex anda phosphorescent compound; a region comprising an acceptor substance;and a compound, wherein a difference between an energy value of anemission of the exciplex and an energy of a peak of an absorption bandhaving the lowest wavelength in an absorption spectrum of thephosphorescent compound is 0.2 eV or less, wherein the light-emittinglayer is between the anode and the cathode, wherein the regioncomprising the acceptor substance is between the anode and thelight-emitting layer, wherein the compound is between the light-emittinglayer and the region comprising the acceptor substance and representedby General Formula (G0):

wherein each of Ar¹ and Ar² independently represents a substituted orunsubstituted fluorenyl group, a substituted or unsubstitutedspirofluorenyl group, or a substituted or unsubstituted biphenyl group,and wherein Ar³ represents a substituent including a carbazole skeleton.23. The light-emitting device according to claim 22, wherein the regioncomprising the acceptor substance is a region comprising a substancehaving a high hole-transport property and the acceptor substance. 24.The light-emitting device according to claim 22, wherein in the regioncomprising the acceptor substance, a layer comprising a substance havinga high hole-transport property and a layer comprising the acceptorsubstance are stacked.
 25. The light-emitting device according to claim22, wherein the region comprising the acceptor substance is in contactwith the anode.
 26. The light-emitting device according to claim 22,wherein a molecular weight of the compound represented by GeneralFormula (G0) is greater than or equal to 500 and less than or equal to2000.
 27. The light-emitting device according to claim 22, wherein thecathode has ytteribium.
 28. A light-emitting device comprising: ananode; a cathode; a light-emitting layer comprising two kinds of organiccompounds which are configured to form an exciplex and a phosphorescentcompound; a region comprising an acceptor substance; and a compound,wherein a difference between an energy value of an emission of theexciplex and an energy of a peak of an absorption band having the lowestwavelength in an absorption spectrum of the phosphorescent compound is0.1 eV or less, wherein the light-emitting layer is between the anodeand the cathode, wherein the region comprising the acceptor substance isbetween the anode and the light- emitting layer, wherein the compound isbetween the light-emitting layer and the region comprising the acceptorsubstance and represented by General Formula (G0):

wherein each of Ar¹ and Ar² independently represents a substituted orunsubstituted fluorenyl group, a substituted or unsubstitutedspirofluorenyl group, or a substituted or unsubstituted biphenyl group,and wherein Ar³ represents a substituent including a carbazole skeleton.29. The light-emitting device according to claim 28, wherein the regioncomprising the acceptor substance is a region comprising a substancehaving a high hole-transport property and the acceptor substance. 30.The light-emitting device according to claim 28, wherein in the regioncomprising the acceptor substance, a layer comprising a substance havinga high hole-transport property and a layer comprising the acceptorsubstance are stacked.
 31. The light-emitting device according to claim28, wherein the region comprising the acceptor substance is in contactwith the anode.
 32. The light-emitting device according to claim 28,wherein a molecular weight of the compound represented by GeneralFormula (G0) is greater than or equal to 500 and less than or equal to2000.
 33. The light-emitting device according to claim 28, wherein thecathode has ytteribium.